Advice needed - changing ST1250 to 9400c but CH doesn't work

[cjbell68]

Terminal 3 on programmer definitely = RED in wiring centre (cable one)
Terminal 4 on programmer definitely = YELLOW in wiring centre (cable one)

Trying to track down a HW OFF wire now - I need to test the two blue wires connected to the programmer's N terminal.

Thanks
Colin

Hmm - just had another look at your diagram, and I'm starting to wonder about the wiring at the programmer. You appear to have three outgoing wires as follows:

1 - Permanent live (fed from L to com link)
2 - N/C
3 - CH on
4 - HW on

So, one would assume that the wire in terminal 3 ends up being red in the wiring centre, 4 as yellow, and then 1 as blue. However, if your diagram of the wiring at the programmer is correct, you would expect terminal 6 to be live all the time.

Can you remove the programmer wiring and do a continuity check end-to-end to confirm?

 

[D_Hailsham]

The wiring is basically correct except as follows.

The ST9400C has 6 terminals:

N: should have two wires - the Supply Neutral; and a link to T2 of the wiring centre (WC/T2).

L: the Supply Live

1 - HW OFF: should connect to the WC/T10
2 - CH OFF: not used
3 - HW ON: should connect to WC/T8
4 - CH ON: should connect to WC/T5


Earthing: Pump T1 seems to be the earth terminal. Is the cable from pump to the boiler a full twin and earth? If so, earthing is OK. But if it's only a twin (L and N) cable, the system is not properly earthed.

 

[cjbell68]

The pump has a white flex with BNE wiring. Neutral and Earth are wired into the block with all the others (boiler, programmer, valve and room stat).

Just got to trace the other end of that blue wire and see if I have a wire I can use for terminal 1 HW OFF - which will then make it fully independent.

Colin

The wiring is basically correct except as follows.

The ST9400C has 6 terminals:

N: should have two wires - the Supply Neutral; and a link to T2 of the wiring centre (WC/T2).

L: the Supply Live

1 - HW OFF: should connect to the WC/T10
2 - CH OFF: not used
3 - HW ON: should connect to WC/T8
4 - CH ON: should connect to WC/T5


Earthing: Pump T1 seems to be the earth terminal. Is the cable from pump to the boiler a full twin and earth? If so, earthing is OK. But if it's only a twin (L and N) cable, the system is not properly earthed.

 

[D_Hailsham]

The pump has a white flex with BNE wiring. Neutral and Earth are wired into the block with all the others (boiler, programmer, valve and room stat).

That's OK, so far as it goes- it connects all the local earth terminals together in the the wiring centre. But where is the connection to the earth for the rest of the house wiring?

Where is the supply for the programmer coming from? It may be the boiler or else a socket/fused spur near the wiring centre. The earth should be coming from this.

Just got to trace the other end of that blue wire and see if I have a wire I can use for terminal 1 HW OFF - which will then make it fully independent.

Be careful. As I said, there should be two wires to the programmer N terminal. It's the HW OFF terminal you need to worry about.

 

[cjbell68]

CONTINUITY TESTING - HW OFF SEARCH:
There are three twin & earth cables behind the programmer.
One pair: Providing Live & Neutral for the programmer.

Second pair: The brown wire goes to HW OFF, the blue is on the N terminal for the programmer.

The third pair are providing CH (BLUE) and HW ON (BROWN) - I managed a continuity test on these earlier today - and the circuits are going on/off with the room and cylinder stat as expected.

My view is the blue wire in the wiring centre could be connected to the N terminal of the programmer - After isolating the programmer I've tried testing for continuity with both of these neutral wires in case the electrician did something weird with the crimps but can't get continuity.

EARTHING:
There is an earth with the RYB wires from the programmer - this is connected into the wiring block. The fused spur for the heating is next to the programmer.

So need to be sure of earth continuity to the rest of the house wiring from the wiring centre, the programmer and the fused spur?

Colin

The pump has a white flex with BNE wiring. Neutral and Earth are wired into the block with all the others (boiler, programmer, valve and room stat).

That's OK, so far as it goes- it connects all the local earth terminals together in the the wiring centre. But where is the connection to the earth for the rest of the house wiring?

Where is the supply for the programmer coming from? It may be the boiler or else a socket/fused spur near the wiring centre. The earth should be coming from this.

Just got to trace the other end of that blue wire and see if I have a wire I can use for terminal 1 HW OFF - which will then make it fully independent.

Be careful. As I said, there should be two wires to the programmer N terminal. It's the HW OFF terminal you need to worry about.

 

[D_Hailsham]

There is an earth with the RYB wires from the programmer - this is connected into the wiring block. The fused spur for the heating is next to the programmer.

So need to be sure of earth continuity to the rest of the house wiring from the wiring centre, the programmer and the fused spur?

The fused spur is almost certainly wired correctly to the rest of the house; so you should need to check the earth there.

It's the cable from the fused spur which concerns me. It's not shown on your diagram. Can you explain where it connects?

 

[cjbell68]

The fused spur is right next to the programmer. I checked the wiring for that this morning, there's a twin&earth feed which looks the same diameter as the feed into the programmer - and there's two other heavier t+e cables that suggest the central heating power is on the ring main and not spurred off.

I'm beginning to think there is either no spare wire available to take the HW OFF 240v to the airing cupboard - or that I need to find those cable joins and check the original wiring to see if there used to be.

There is one other possibility that has occured to me. I know there are four wires for the boiler - EARTH, a separate switch live & pump-overun live and also a blue wire that is currently connected to neutral at the wiring centre. I would expect this cable to be routed directly from the boiler to the airing cupboard - but if it was routed via the programmer there is a possibiilty the neutral wire from this cable (cable three) is connected to terminal 1 at the programmer so the 240v would flow to the neutral block at the wiring centre.

I'd be grateful for someone to read the above supposition and let me know if there are any errors in the reasoning - thanks.

Colin

There is an earth with the RYB wires from the programmer - this is connected into the wiring block. The fused spur for the heating is next to the programmer.

So need to be sure of earth continuity to the rest of the house wiring from the wiring centre, the programmer and the fused spur?

The fused spur is almost certainly wired correctly to the rest of the house; so you should need to check the earth there.

It's the cable from the fused spur which concerns me. It's not shown on your diagram. Can you explain where it connects?

 

[cjbell68]

Hi,
Checking back through the thread and don't think I responded to this.

I should have mentioned this - I removed the link between live and terminal one as a chap from Honeywell explained it wasn't necessary to make the bridge as the 9400c provides 240v out on this terminal - the ST1250 didn't.

In anycase I don't think this wire was doing anything useful in the old set-up as the programmer didn't support independent CH anyway - it has a HW / HW+CH mechanical switch on the side!

So - now I have the new wiring in place there is just a single wire connected to terminal one that I would expect to connect to the blue wire on terminal 6 in the wiring centre, but as discussed with D_Hailsham I can't confirm continuity so I need to double check the wiring behind the programmer and maybe have to start digging into the wall in the utility room to find the joints.

Colin

Hmm - just had another look at your diagram, and I'm starting to wonder about the wiring at the programmer. You appear to have three outgoing wires as follows:

1 - Permanent live (fed from L to com link)
2 - N/C
3 - CH on
4 - HW on

So, one would assume that the wire in terminal 3 ends up being red in the wiring centre, 4 as yellow, and then 1 as blue. However, if your diagram of the wiring at the programmer is correct, you would expect terminal 6 to be live all the time.

Can you remove the programmer wiring and do a continuity check end-to-end to confirm?

 

[D_Hailsham]

This contains replies to several posts.

There are three twin & earth cables behind the programmer.
One pair: Providing Live & Neutral for the programmer.

One question answered.

Second pair: The brown wire goes to HW OFF, the blue is on the N terminal for the programmer.

You need to find the other end of this cable. The brown wire should connect to WC/T10. The blue should connect to WC/T2.

The third pair are providing CH (BLUE) and HW ON (BROWN) - I managed a continuity test on these earlier today - and the circuits are going on/off with the room and cylinder stat as expected.

Your last diagram shows a yellow wire connected to the programmer. What has happened to it?

My view is the blue wire in the wiring centre could be connected to the N terminal of the programmer - After isolating the programmer I've tried testing for continuity with both of these neutral wires in case the electrician did something weird with the crimps but can't get continuity.

By N terminal I hope you mean terminal 2. The blue wires connected to other terminals are not neutrals

There is an earth with the RYB wires from the programmer - this is connected into the wiring block.

Which terminal does it connect to in the wiring centre?

What RYB wire are you talking about? You said above that there are three cables to the programmer; none of them has a red or a yellow wire.

Just a thought. Is the RYB cable visible only at the wiring centre end, i.e there is a hidden connection between the brown/blue cables at the programmer and the RYB cable at the wiring centre?

So need to be sure of earth continuity to the rest of the house wiring from the wiring centre, the programmer and the fused spur?

Yes. Terminal one of the wiring centre is the earth point for the pump and the motorized valve so this needs a connection to the main earth, possibly via the programmer or the boiler earth point.

The fused spur is right next to the programmer. I checked the wiring for that this morning, there's a twin&earth feed which looks the same diameter as the feed into the programmer - and there's two other heavier t+e cables that suggest the central heating power is on the ring main and not spurred off.

That's no problem.

I'm beginning to think there is either no spare wire available to take the HW OFF 240v to the airing cupboard - or that I need to find those cable joins and check the original wiring to see if there used to be.

See above.

There is one other possibility that has occured to me. I know there are four wires for the boiler - EARTH, a separate switch live & pump-overun live and also a blue wire that is currently connected to neutral at the wiring centre. I would expect this cable to be routed directly from the boiler to the airing cupboard - but if it was routed via the programmer there is a possibility the neutral wire from this cable (cable three) is connected to terminal 1 at the programmer so the 240v would flow to the neutral block at the wiring centre.

There are three pump connections on the boiler: Live, Neutral and Earth. I think you will find that the blue wire connects to the Neutral. Find the boiler end of the cable and check, it quite easy to do as the same cable has a yellow.

You don't show what the boiler earth cable connects to in your diagram.

I removed the link between live and terminal one as a chap from Honeywell explained it wasn't necessary to make the bridge as the 9400c provides 240v out on this terminal - the ST1250 didn't.

Correct. The link is not needed.

So - now I have the new wiring in place there is just a single wire connected to terminal one that I would expect to connect to the blue wire on terminal 6 in the wiring centre

Terminal 1 of the programmer should connect to terminal 10 of the wiring centre.

 

[cjbell68]

Hi, thanks for coming back - in case I've not said it already I really appreciate the comments and suggestions that you and others are giving me

First an apology - I'll try to be clearer when describing the wires whether I'm refering to connecting something at the wiring centre (WC) terminals 1-10, or the programmer terminals LN1234.

To help I've made my comments against each of your responses in the quote below - highlighted in bold to stand out.
For information when continuity testing I am using an autoranging multimeter from screwfix and I'm using the resistance setting to check - gives O.L when no link, 0 when good continuity or varying readings for somewhere inbetween.

This contains replies to several posts.

There are three twin & earth cables behind the programmer.
One pair: Providing Live & Neutral for the programmer.

One question answered.

Second pair: The brown wire goes to HW OFF, the blue is on the N terminal for the programmer.

You need to find the other end of this cable. The brown wire should connect to WC/T10. The blue should connect to WC/T2.

I tested brown wire at terminal 1 of the programmer to see if it matched the blue wire at the WC end which was in WC/T6. I'm testing using resistance and I get a figure ~12M ohm. I may be wrong here but I assumed that maybe I've identified that it is the brown wire from programmer/T1 - but perhaps there is some kind of cable fault. Not sure.

I connected the blue wire from WC/T6 to WC/T10 then fired the system up with CH circuit on, HW circuit off at the programmer - demand from the room stat - no demand from cylinder stat. I tested WC/T10 against neutral and got a reading of ~65v.

I repeated the above test but took the blue wire away from WC/T10 and isolated it back at WC/T6.

Readings
WC/T10 against neutral ~65v
WC/T6 against neutral ~20v - if identified correctly and no cable faults I would expect 240v here - fed from programmer T1 for HW OFF.

The third pair are providing CH (BLUE) and HW ON (BROWN) - I managed a continuity test on these earlier today - and the circuits are going on/off with the room and cylinder stat as expected.

Your last diagram shows a yellow wire connected to the programmer. What has happened to it?

The main picture block shows the wiring I have identified at the wiring centre. The bottom right hand corner shows the wiring numbers & colours at the programmer end. As mentioned earlier I believe I am correct to say:
Programmer T3 CH ON = BLUE WIRE -> RED wire at WC end (W07) from cable one connected to WC/T5 providing 240v for switching through the room stat.

Programmer T4 HW ON = BROWN WIRE -> YELLOW wire at WC end (W09) from cable one connected to WC/T8 and providing 240v for switching through the cylinder stat.

I believe these two wires are correctly identified as I can fire the HW / CH independently - or together by switching the room / cylinder stat demands on/off. Note HW circuit must be on in order to get the CH working as can't get a voltage to the grey wire.

My view is the blue wire in the wiring centre could be connected to the N terminal of the programmer - After isolating the programmer I've tried testing for continuity with both of these neutral wires in case the electrician did something weird with the crimps but can't get continuity.

By N terminal I hope you mean terminal 2. The blue wires connected to other terminals are not neutrals

To clarify the N terminal at the programmer end (as in ENL1234) - I am not confusing this with the programmer terminals 1234.

There is an earth with the RYB wires from the programmer - this is connected into the wiring block.

Which terminal does it connect to in the wiring centre?

All earth wires arriving at the wiring centre are connected to WC/T1. I have added the wires - and I show that they are connected to WC/T1 in the schematic top right - but I have not drawn the lines in on the circuit diagram. I have not tested the earth wires for continuity at the WC.

What RYB wire are you talking about? You said above that there are three cables to the programmer; none of them has a red or a yellow wire.

Just a thought. Is the RYB cable visible only at the wiring centre end, i.e there is a hidden connection between the brown/blue cables at the programmer and the RYB cable at the wiring centre?

Yes - the cables have been crimped - these joints are somewhere behind plaster in my utility room!

So need to be sure of earth continuity to the rest of the house wiring from the wiring centre, the programmer and the fused spur?

Yes. Terminal one of the wiring centre is the earth point for the pump and the motorized valve so this needs a connection to the main earth, possibly via the programmer or the boiler earth point.

As mentioned I'm fairly confident there is earth continuity from spur to the programmer then through to WC/T1 for the other devices but have not tested this.

The fused spur is right next to the programmer. I checked the wiring for that this morning, there's a twin&earth feed which looks the same diameter as the feed into the programmer - and there's two other heavier t+e cables that suggest the central heating power is on the ring main and not spurred off.

That's no problem.

I think this the source of earth for the HW/CH system - possibly at the boiler end as well but have not opened that up.

I'm beginning to think there is either no spare wire available to take the HW OFF 240v to the airing cupboard - or that I need to find those cable joins and check the original wiring to see if there used to be.

See above.

There is one other possibility that has occured to me. I know there are four wires for the boiler - EARTH, a separate switch live & pump-overun live and also a blue wire that is currently connected to neutral at the wiring centre. I would expect this cable to be routed directly from the boiler to the airing cupboard - but if it was routed via the programmer there is a possibility the neutral wire from this cable (cable three) is connected to terminal 1 at the programmer so the 240v would flow to the neutral block at the wiring centre.

There are three pump connections on the boiler: Live, Neutral and Earth. I think you will find that the blue wire connects to the Neutral. Find the boiler end of the cable and check, it quite easy to do as the same cable has a yellow.

You don't show what the boiler earth cable connects to in your diagram.

As above - all the earths are to WC/T1

Regarding tracing the boiler cable - I checked the blue neutral at the wiring centre end (W04) and this is connected to the N terminal at the programmer - I do not know if the boiler wiring for EARTH, switch live and pump live are routed direct from the boiler to the WC or if they go via the site of the old programmer in the utility room and so are not accessible to me. I do not believe they can come near the new programmer site because the boiler operates correctly and there are no other wires available at the programmer end.

I removed the link between live and terminal one as a chap from Honeywell explained it wasn't necessary to make the bridge as the 9400c provides 240v out on this terminal - the ST1250 didn't.

Correct. The link is not needed.

I tried re-establishing the link to rule out the 9400c being faulty and not providing the 240v from programmer T1. I tested the blue wire at WC/T6 to see the results - no change to any voltages at WC/T10 or WC/T6.

So - now I have the new wiring in place there is just a single wire connected to terminal one that I would expect to connect to the blue wire on terminal 6 in the wiring centre

Terminal 1 of the programmer should connect to terminal 10 of the wiring centre.

I've tried this - see earlier notes - getting a voltage from the blue wire of ~20v - not 240v, suggesting I didn't identify the wire correctly or maybe some kind of fault

 

[D_Hailsham]

First an apology - I'll try to be clearer when describing the wires whether I'm refering to connecting something at the wiring centre (WC) terminals 1-10, or the programmer terminals LN1234.

That's helpful, but no need to apologise,I'm just as guilty of causing confusion - see later.

I tested brown wire at terminal 1 of the programmer to see if it matched the blue wire at the WC end which was in WC/T6. I'm testing using resistance and I get a figure ~12M ohm. I may be wrong here but I assumed that maybe I've identified that it is the brown wire from programmer/T1 - but perhaps there is some kind of cable fault. Not sure.

A reading of 12Mohm is 12 million ohms, which is effectively an open circuit

I connected the blue wire from WC/T6 to WC/T10 then fired the system up with CH circuit on, HW circuit off at the programmer - demand from the room stat - no demand from cylinder stat. I tested WC/T10 against neutral and got a reading of ~65v.

Are you 100% certain that the blue wire connected to WC/T6 connects back to Programmer/T1 (HW OFF)?

I repeated the above test but took the blue wire away from WC/T10 and isolated it back at WC/T6.

Readings
WC/T10 against neutral ~65v
WC/T6 against neutral ~20v - if identified correctly and no cable faults I would expect 240v here - fed from programmer T1 for HW OFF.

The reading of ~65v on WC/T10 is normal. It's due to the way the mid-position valve works. See How the mid position valve works

The main picture block shows the wiring I have identified at the wiring centre. The bottom right hand corner shows the wiring numbers & colours at the programmer end.

There are two boxes at the bottom of the diagram - one refers to the "existing programmer", the other to the ST1250. Is the existing programmer the ST1250 or the ST9400C?

I believe I am correct to say:
Programmer T3 CH ON = BLUE WIRE -> RED wire at WC end (W07) from cable one connected to WC/T5 providing 240v for switching through the room stat.

NO! If you are talking about the ST9400C, Programmer T3 is HW ON.

Programmer T4 HW ON = BROWN WIRE -> YELLOW wire at WC end (W09) from cable one connected to WC/T8 and providing 240v for switching through the cylinder stat.

ST9400C/T4 is CH ON not HW ON.

By N terminal I hope you mean terminal 2. The blue wires connected to other terminals are not neutrals

To clarify the N terminal at the programmer end (as in ENL1234) - I am not confusing this with the programmer terminals 1234.

Now I'm confusing you! When I said terminal 2, I meant WC/T2, not the neutral terminal of the ST9400C.

All earth wires arriving at the wiring centre are connected to WC/T1. I have added the wires - and I show that they are connected to WC/T1 in the schematic top right - but I have not drawn the lines in on the circuit diagram. I have not tested the earth wires for continuity at the WC.

If all earth wires, from pump, boiler, valve, programmer and thermostats connect together at WC/T1, then everything is OK. It's just that they are not all show on your diagram.

Yes - the cables have been crimped - these joints are somewhere behind plaster in my utility room!

Another mystery solved - or is it created???

As mentioned I'm fairly confident there is earth continuity from spur to the programmer then through to WC/T1 for the other devices but have not tested this.

As long as you are happy

Regarding tracing the boiler cable

No need to do this any more - the cable is OK

I tried re-establishing the link to rule out the 9400c being faulty and not providing the 240v from programmer T1. I tested the blue wire at WC/T6 to see the results - no change to any voltages at WC/T10 or WC/T6.

If there is no voltage at WC/T6 then with the link in place or HW OFF, then either the wire does not go from HW OFF to WC/T6 or the programmer is faulty.

Terminal 1 of the programmer should connect to terminal 10 of the wiring centre.
I've tried this - see earlier notes - getting a voltage from the blue wire of ~20v - not 240v, suggesting I didn't identify the wire correctly or maybe some kind of fault

I agree, I think either the wire has not been correctly identified, ot there is a fault in the programmer.

You need to find out which it is, or you will just keep going round in circles.

 

[cjbell68]

Hi again D_Hailsham

Just a copy/paste of what I think are the most relevant questions / comments this time to cut down on the post length!

Are you 100% certain that the blue wire connected to WC/T6 connects back to Programmer/T1 (HW OFF)?
No I'm not sure - ties in with your comment about the high resistance. Thanks for the link to the mid pos valve workings explains that voltage.

There are two boxes at the bottom of the diagram - one refers to the "existing programmer", the other to the ST1250. Is the existing programmer the ST1250 or the ST9400C?
Both boxes refer to the wiring as it was setup for the ST1250.
You're spot on about the terminal outputs for 9400c - I'm going to double check the wires from the programmer for CH & HW on and make sure get the diagram correct. I'll also add in the connections from the earth wires to WC/T1 for completeness.

Now I'm confusing you! When I said terminal 2, I meant WC/T2, not the neutral terminal of the ST9400C.
I see - you were talking about the WC end and I was talking about the programmer end. I was trying to see if one of the wires at the programmer neutral terminal turned out to be continuous with the blue wire that is on WC/T6 in my diagram.

So in summary.
1. Will double check relationship between terminals 3&4 at 9400c with WC/T5 & WC/T8 and update diagram including showing the earth connections to WC/T1.

2. I cannot be sure that the blue wire at WC/T6 is accessible at the programmer.

3. I think once I have identified the terminal 3 & terminal 4 wires correctly at WC I will disconnect the HW ON wire from 9400c/T3 and WC/T8 and make a connection 9400c/T1 to WC/T10 so I can check the 9400c is providing HW OFF signal with 240v for the grey wire.

4. I'll probably pull the fridge freezer out, get behind the plaster and check the incoming/outgoing wires out

Appreciate your thoughts - thanks again for your help - if nothing else I have a much better understanding of the Y plan circuit - even though I mixed up the HW / CH ON terminal designations!
Colin

 

[D_Hailsham]

Are you 100% certain that the blue wire connected to WC/T6 connects back to Programmer/T1 (HW OFF)?
No I'm not sure - ties in with your comment about the high resistance.

Need checking. Disconnecting all wires at one end of a cable, linking two and then checking for continuity at the other end is the best way - but not easy if the wires change colour behind a wall! You may have to test more than one pair in a cable in case there is a dodgy connection mid-way!

There are two boxes at the bottom of the diagram - one refers to the "existing programmer", the other to the ST1250. Is the existing programmer the ST1250 or the ST9400C?
Both boxes refer to the wiring as it was setup for the ST1250.

So why are they different?

I was trying to see if one of the wires at the programmer neutral terminal turned out to be continuous with the blue wire that is on WC/T6 in my diagram.

Got you!

1. Will double check relationship between terminals 3&4 at 9400c with WC/T5 & WC/T8 and update diagram including showing the earth connections to WC/T1.

Good idea.

2. I cannot be sure that the blue wire at WC/T6 is accessible at the programmer.

Needs checking, if it is just a Neutral, back to Programmer N then it should be linked to WC/T2.

3. I think once I have identified the terminal 3 & terminal 4 wires correctly at WC I will disconnect the HW ON wire from 9400c/T3 and WC/T8 and make a connection 9400c/T1 to WC/T10 so I can check the 9400c is providing HW OFF signal with 240v for the grey wire.

Sensible approach at least you know the wire is OK.

4. I'll probably pull the fridge freezer out, get behind the plaster and check the incoming/outgoing wires out

Do the continuity checks first.

 

[cjbell68]

Hi
Off to do the checks when the rads & hot water are satisfied...

You asked why the two diagrams for the ST1250 at the bottom right of the picture were different - the left diagram is a sticker that is on the back of the ST1250 programmer which I presume shows the way it uses the outputs, the other one is a diagram showing the way the wiring was connected to the back of the ST1250 (via the backplate).

Will let you know how I get on after the continuity test - definitely going to get those checks and updates done before going on a hunt behind the plaster

 

[cjbell68]

Hi

1. Continuity testing to check which cable is which.
I tested the two neutrals at the 9400c for continuity. One of them goes to WC/T2. The other tested good for continuity with a neutral from the the fused switch.

I then used the neutral wire from 9400c/N which goes to WC/T2 to check the HW & CH on wires. I also connected those two wires together at the WC end and tested them for continuity at 9400c/T3 and T4. From these three checks I got:

9400c/T3 = HW ON = Brown = cable one W07 Red which is connected to WC/T5 (room stat!)

9400c/T4 = CH ON = Blue = cable one W09 Yellow which is connected to WC/T8 (cylinder stat!)

The implication is that the wires I have at 9400c/T3 and 9400c/T4 need to be swapped over. The chap at Honeywell said when I changed from the ST1250 it would be 3-->3 and 4-->4, but if the WC wiring is correct I don't see how that can be. Doesn't help I can't find a wiring diagram for the ST1250 anywhere on the web. In the end I just need to be sure I get 240v from 9400c/T1/T3 and T4 when I need them, and to the right terminals at the WC.

I updated the diagram to show the current wiring, added the earth connections to WC/T1 and also made some notes about the continuity testing (I included a retest of all three thermostat cores).

Note there remain assumptions as to which terminal of the cylinder stat is which because I've not taken it apart in case it won't go back together again!

So I have one spare wire at the WC that I can't find the other end of, and a similar wire at the 9400c (connected to HW OFF) that I can't find the other end of!!

2. Still can't find the other end of the wire parked at WC/T6!

3. Test 9400c HW OFF produces 240v
I took the wire from 9400c/T3 and connected it to 9400c/T1 and at the other end to WC/T10. I set HW circuit off, CH circuit on and no demand from the cylinder. The grey wire was live with 240v so I assume the HW OFF output works on the 9400c.

4. Checking the crimp joints...
Given the time and what I found so far I'm not going behind the fridge yet!
I think the next thing maybe is to correct the wiring error by swapping the wires at 9400c/T3 and T4 then testing how it all works.
Had enough for this evening!

Hope its clear - questions and comments are welcome!

Thanks

Colin

Untitled

• cjbell68
• 15 Mar 2010
• 1