Heating only comes on when hot water is also selected

[pns1953]

Hi, I would be grateful for some thoughts on this issue in my CH system.

The problem:
I can only get the heating to work (boiler firing up and rads heating) if the programmer is also set to have the hot water on (not necessarily calling for heat - just on). This was the situation when I moved in here 6 months ago so I don't know if it's always been like that or a fault that has developed previously - I suspect that the system is probably 12 - 15 years old.

The system appears to be a Sundial Y plan - I have a Honeywell V4073a mid-position valve, and what appears to be a Honeywell ST699 programmer, plus the usual tank and room stats.

I am trying to determine if the problem is with the valve, the programmer, or both.

I've checked the very useful website on what should happen in a Y-plan system, http://octaveblue.co.uk/c_heating/index.htm

I've also attempted to understand how the valve itself works, http://www.diyfaq.org.uk/plumbing/controls/midpositionvalve.htm, but probably don't fully understand the exact sequence of operations!

I've also checked Honeywell's own FAQ on the valve: http://www.honeywelluk.com/documents/All/pdf/975.pdf

I've measured the voltages between neutral and each of the white, grey and orange connections to the valve, and will summarise these below for various programmer combinations (absolute values are probably subject to some error as it's just a cheap multimeter):

1) HW off, CH on and calling for heat: Programmer CH LED comes on and relay clicks, but no movement from valve and boiler doesn't fire up

White: 248v, Grey: 63v, Orange: 128v


2) HW on but not calling for heat, CH on and calling for heat:
Valve moves, boiler fires up, heating works normally

White: 245v, Grey: 248v, Orange: 248v

3) HW on, calling; CH on, calling:
Valve moves again, presumably to mid-position as both CH and HW work as expected

White: 248v, Grey: 66v, Orange: 248v


OK, that's the facts of the matter. As for trying to work out what's at fault -

In scenario 1) My understanding is that the voltage I'm measuring on the grey wire is the output from the programmer 'HW OFF' connection. it is 63v when it should be live. Grey and white are the control inputs to the valve. In this situation Orange should also be live (to fire the boiler) but it's 128v.

In scenario 2), when I turn the programmer so that as well as CH on and calling, HW is also on (but not calling for heat) then grey, white and orange are all live as expected, and everything works as expected.

My presumption is that there is a fault in the programmer - possibly a sticky relay feeding the HW-OFF output, or something else that's failed.

I can't see how I should ever get a voltage of 66/63v on the grey wire.

However, I am wondering if the valve powerhead itself is also faulty since I can't see how in scenario 1) I should get an output of 128v on the orange connection; according to the details of operation of the valve, in this scenario, both white and grey should be live, and this will connect the orange output to live via the internal SW2 of the valve. However in my case, grey ISN'T live but 63v so maybe the internal operation of the valve is affected - but I still can't understand orange being 128v not 0 or 245!

OK. Sorry for the long (but hopefully logical) post.

Although I need a plumber for some additional work, changing the powerhead or the programmer is something I can do myself. They are of course both expensive components, so I would very much welcome any thoughts or opinions as to which is at fault - or most likely to be. My money is still with the programmer at least - maybe the powerhead too.
I may have missed some diagnostic steps but can check other things too if anyone thinks it's worthwhile.

Thanks in advance ....
Phil

 

[footprints]

Hi Phil,
Nine times out of ten it’s a faulty valve, either the head faulty or the body stuck.

You will boggle your mind trying to sort out what’s happening with a meter! At the halfway point the power is cut off and a small DC voltage holds the motor in a stalled position, don’t even go there!

Do what 99.99% plumbers/ gasfitters do get the Y plan valve changed and hope it sorts it out, you can try moving the valve with the manual lever over in the power off situation and see if it returns freely, but that’s not a guarantee that it in fact moves all the way under it’s own power as the lever is only designed to lock the valve in the mid position.

Early valves need to be changed in full, later ones can have the head alone changed if that’s at fault.

P.S.
Programmer needs to supply a CH on output & HW on and HW off output. Likewise for the CH room stat and HW stat outputs. To check those components it’s easier to do if you disconnect the valve wires to avoid confusion of power fed back.

Regards,
footprints

 

[MANDATE]

Read your post with interest!
The voltage on the HW OFF wire should be 240v. I think you need to test this at the programmer and the terminal box. sounds like poor connection.
Note this wire joins another from the cylinder stat, so it might join it at the terminal box or at the cylinder stat.
Of course it could be a intermittent connection as it appears the valve sometimes moves fully across to CH position.

The start or rest position for the valve is HW, but if CH had been ON previously and switched off by the programmer or room stat it cuts the power on the white wire(which leads to the orange through a micro switch) so boiler stops, but because the grey is still live the valve stays at CH position.
This can be misleading if it's not clear where the valve is.

The power to light the boiler goes from the HW ON terminal on the programmer to cylinder stat for both HW and HW/CH, but when HW is satisfied or turned off and CH is the only demand, then power goes from CH ON terminal to room stat and then to valves white wire, then through a micro switch(when triggered) and out though the valves orange wire.
A second micro switch is fed with separate power supplies. power on the white which drives to it mid point only and if the grey is live it will carry on to CH position.
Of course if the grey is not live the valve will stay at mid position.

This mid position of course is only temporary, it continues only until either CH or HW becomes satisfied. It then either drops back to HW only or moves forward to CH only

Sometimes the valve spindle is too stiff and too much resistance for the motor.
Sometimes the motor is the problem, if there is no movement at all.
Sometimes the problem is down to the micro switches.
Sometimes gear teeth on quadrant /motor causes resistance
I had a case where the valve moved as it should, but no output from orange wire. As suspected micro switch contacts dirty/burnt.
There are 4 pairs of contacts any of which may not make or break when faulty.
Replacing the actuator head does have its advantages.

 

[MANDATE]

If you do a search in the 'plumbing and central heating' section for the author 'curious' it may be of interest

 

[pns1953]

Many thanks both of you for your replies.
I've not had the time to fiddle more in the last couple of days (partly because of an unexpected spatial conjunction between my car and a left-hand drive HGV on a roundabout )

The post by 'curious' ( //www.diynot.com/forums/viewtopic.php?p=40979#40979 ) was indeed interesting, though I haven't followed through all the details. I'm thinking that the explanation of the 'floating' grey wire probably explains some but not necessarily all of the 'odd' voltages I'm seeing (I'm not sure whether there's a legitimate reason that I should get 128v appearing in Orange in my 'scenario 1' - maybe that's because I've not yet stared at the diagrams enough ...)

Just another observation or two about the behaviour of my system -
As far as I can tell, as long as the programmer has both CH and HW in an 'on' period, then the mid-position valve does appear to behave as expected depending on whether the tank or room stats, or both, are calling for heat. The boiler fires and the relevant ports of the valve heat up.

That was why my initial feeling was that the valve + actuator did seem to be behaving correctly.

The suggestion of disconnecting the actuator wiring from the connector block (a rats-nest of unlabelled cables connected using 'chocolate block' in my case!) seems sensible and I'll give that a go when I have a bit more time.

What isn't clear to me is what voltage I should see at the DHW OFF terminal of the programmer.

When I'm in a timed period for HW, I do indeed appear to see grey as 'live' as the diagrams indicate (my scenario 2) . However, when HW is in an OFF period on the programmer, (my scenario 1) then this output (or at any rate the grey wire to which it is connected) does appear to be floating. Is that normal, or should I see that 'HW OFF' should still be live even during an 'off' timed period?

As to possible bad connections - I was a bit surprised that the connections between the programmer & its back-plate just seemed to rely on the 8 solder-pads on the PCB pressing against the screw terminals on the backplate. I thought I might have found the cause as the unused backplate terminal screws hadn't been tightened and were a bit 'high' - but it didn't make any difference. I've also checked all the connections in the choc-block strip and they were all tight.

Thanks again for your help
Phil

 

[footprints]

If the valve is disconnected from the system so no confusing signals from there, HW off terminal will simply be 240 or 0 depending on the position it's in.

 

[pns1953]

OK thanks, disconnecting the actuator definitely seems to be the next logical step, I'll see if I can find time this weekend to give it a go!

 

[MANDATE]

Another point I overlooked earlier regarding the valves grey wire.
There are 'two' power supplies to the grey.
There is the supply from the programmers HW OFF terminal for use when the HW is not switched ON.
Then there is a supply via a different route when the HW is ON. This is through the cylinder stat. the cylinder stat is basically a two way switch.
So power starts at the programmer HW ON and goes to the common terminal of the stat, then across the stat to the 'not satisfied terminal' and on to fire the boiler. Now when HW becomes 'satisfied' this link is broken and a new link is created from 'common to the 'satisfied terminal' and a wire from this terminal goes to the grey.
Now if the contacts between 'common' and the 'satisfied terminal' are dirty/burnt then power to the 'grey' wire would be affected and the valve could not continue from mid position. Of course this is because the HW although satisfied it is still switched ON. It is only when HW is switched OFF that this route through the cylinder stat becomes in active and is replaced by the wire from programmer HW OFF to the valves grey wire.

Regarding poor connections, besides loose connections, there's a possibility the wires may be in the terminals too far and securing screws are tightened on the insulation.
I bench tested a new head before fitting it and verified it worked correctly by applying switched power supplies to 'white' and 'grey' wires and simulating its working actions and observing the valves movements

 

[bellairaphon]

Have you checked connections in the cylinder stat?

 

[pns1953]

Well, the weather was much too nice this weekend to spend time grovelling around in the airing cupboard!

But I will be back...
I will also disconnect the cylinder stat & check that's working OK.

 

[pns1953]

Well I eventually got around to trying to sort out this issue -

With the aid of the diagrams on the http://octaveblue.co.uk/c_heating/index.htm site I did a bit of tracing and worked out what was what in my rather horrible connector block:

Untitled

• pns1953
• 13 Jul 2013
• 1

I also did check the cylinder thermostat as suggested - although it's old, it was working OK.

Once I'd got a good idea of the wiring, and had another look at the backplate of the programmer, I spotted what should have been obvious to me from the start:

Untitled

• pns1953
• 13 Jul 2013
• 1

There was no connection between contact 7 on the backplate (labelled as HW/Normally Closed, which I eventually realised was the HW-OFF output) and the grey lead on the valve (as shown here. )

I suppose it should have been obvious to start with, but I didn't associate the labelling in the backplate with that in the web link above.

Anyway, I connected a spare bit of cable between the programmer and the grey valve wire, and voila!
The heating now works independently of the hot water, which thus solves my initial problem.

I'll have to tidy things up, it's odd, the multicore cable between the programmer and the junction box has had a spare core cut off. I notice that the Honeywell instructions for the ST699 programmer say "If used to provide time control for a gravity hot water/pumped heating system, it is not possible to select Heating only without Hot Water"

That seems to be what was happening, so maybe my system was converted to fully-pumped at a later stage and the wiring not re-done correctly.
With luck the existing cable can has enough slack that I can re-terminate the ends and regain the extra core to make the necessary connection.

Once I've done that I'll be able to have heating on independently of the hot water; the main point of this exercise is that I want to replace my old room stat with a Honeywell CM907 programmer, which would mean leaving the main programmer switched to 'ON' all the time as the heating periods are controlled by the CM907 - I didn't want to have to leave the hot water on constant too.

So - thanks to all for your comments and assistance.
I've avoided having to purchase any replacement parts as everything seems to be working - and I've learned a bit about my system into the bargain!

Phil

 

[MANDATE]

Good to hear you got it sorted. It's not the first time the HW OFF wire did not exist.