Heating Won't Come On as per Programmer

[OscarFoxtrot]

Hello,

A little under a year ago D_Hailsham kindly offered some help on the same problem I currently have. A new baby arrived followed by summer and I never got round to sorting it.

Original Thread - //www.diynot.com/forums/plumbing/ch-not-working-to-programmer-instruction.393190/

Basically the heating will only come on if I 'force' it by turning the thermostat down past 'below' then turning it quickly back up to the required temperature. Without doing that it will not come on as requested at the programmer. HW works as it should.

Boiler is a Glow Worm Flexicom 15HX installed in Dec 2007 (original paperwork present).

Its controlled by a Potterton EP2002 programmer directly below the boiler (in the kitchen) with a Potterton thermostat in the hall by the radiator with the two lock shields.

I bought a replacement MPE322 but haven't installed it yet. Before I do I was wondering if anyone had any other thoughts on what might be the problem?
Old thermostat? Wiring issue (although I suspect the wiring is as it was when the house was built in 1998)?

Cheers

 

[Boilerman2]

Without attending site and carrying out electrical checks to see where the fault actually lays, it is only possible to guess- which could end up costing you more in the long run, I have known the Potterton Electronic Rooms stat to suffer from a sticking relay - of course that is only a guestimate

 

[OscarFoxtrot]

Understood boilerman, cheers!

Having just redecorated the hall that old stat isn't looking to good so happy to replace anyway.

Any recommendations on a new stat? Not too sure how they work with an existing programmer but is a programmable stat a good option? Would CH on the existing programmer need to be set to On?

 

[flameport]

Would CH on the existing programmer need to be set to On?

Yes - a programmable thermostat does both time and temperature so the programmer should be set On permanently, or alternatively wired to be on all the time, or replace it with a single channel model which will do the hot water only.
Just remember that it is then a case of setting what temperature you want at different times/days - not 'heating will switch on at X hour'.

As for which one - many different manufacturers and models available.
I have a Danfoss TP7001M which unlike most is mains powered and does not require batteries.
This may or may not be suitable for you.

 

[D_Hailsham]

Just re-read the original topic.

I asked you to check how many wires are connected to the thermostat on the side of the cylinder. Did you do this? If so, how many wires?

I didn't pick up the problem with the room stat. However, that would have nothing to do with the fact that you can only get CH when the HW is turned off.

 

[jeff the gasman]

This problem can be caused by incorrect wiring to the room thermostat ie
The anticipator is constantly live.
Always worth checking.
Jeff

 

[OscarFoxtrot]

Thank you all for the replies and advice.

Some photos for your perusal:


Room Stat

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• OscarFoxtrot
• 3 Jan 2015
• 1

Wiring Centre

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• OscarFoxtrot
• 3 Jan 2015
• 1

Cylinder Stat

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• OscarFoxtrot
• 3 Jan 2015
• 1

3Port Valve

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• OscarFoxtrot
• 3 Jan 2015
• 1

 

[OscarFoxtrot]

Any thoughts?

Cheers

 

[D_Hailsham]

In your earlier topic I asked you to carry out some tests, which you did, and these were the results:

Turned everything off. That reset the valve
HW to on, stat to max - pipe to cylinder got real hot. OK
CH to on, stat to max - both pipes now hot. OK
HW stat to min - boiler stops Wrong
Turned HW stat to max - boiler fired OK
HW off - boiler running CH OK

So everything is correct except when CH is called and HW is satisfied. This normally means that there is no wire from the cylinder stat SAT terminal to the valve grey wire. Looking at the picture, the cylinder stat does have a wire connected to the SAT terminal. It would be worth checking the other end. It should go to the same terminal as the valve's grey wire. There will be a third wire on the terminal, coming from the Programmer HW OFF terminal.

If the wires are in place, the only possible cause of your problem is a faulty cylinder stat.

 

[OscarFoxtrot]

Thanks again for taking the time to reply.

Please see attached a photo of the wiring at the programmer.

Is this where you mean for the other end of the wire to the SAT terminal?

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• OscarFoxtrot
• 5 Jan 2015
• 1

 

[D_Hailsham]

Do the cylinder stat and motorized valve cables connect directly to the programmer or via a junction box?

Direct
Does the valve grey wire connect to terminal 1?
Does the HW stat SAT terminal connect to terminal 1?

via Junction box
The valve grey wire + wire from prog T1 + wire from HW stat SAT should all connect to the same terminal in the junction box.

 

[OscarFoxtrot]

Hopefully I'm seeing this properly.

The blue wire from SAT (C, 2 - Correct?) is connected to the grey wire from the motorised valve at position D of the wiring centre. There are no other wires present at that terminal. There are also no wires present at terminal 1 of the programmer.

There are
3 x N
3 x L
1 x Blue at 3
1 x Yellow at 4
2 x Reds at 5

 

[D_Hailsham]

The blue wire from SAT (C, 2 - Correct?) is connected to the grey wire from the motorised valve at position D of the wiring centre. There are no other wires present at that terminal. There are also no wires present at terminal 1 of the programmer.

Yes, C2 is the SAT terminal.

When you say "wiring centre", I assume you are referring to the backplate to which the EP2002 programmer is attached.

The link from Valve grey to C/2 at D is correct. You also need to link terminal 1 to D as well. Your problem should then be solved.

 

[OscarFoxtrot]

Unfortunately not. For wiring centre I was meaning the big junction box below the cylinder stat.

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• OscarFoxtrot
• 7 Jan 2015
• 1

The cylinder, stat and big junction box are in a cupboard upstairs whilst the programmer is below the boiler in the kitchen downstairs.

Thanks again for your help.

So it seems there is no link between Terminal 1 at the programmer downstairs and Valve Grey/C2 upstairs. Its either never been done or is wired incorrectly to another terminal. Although the boiler itself has been replaced It must have always had this problem then as none of the wiring appears to be new nor are any of the controls/stats/programmers.

Anything else I can do or look at or is there any possible work around?

 

[D_Hailsham]

Unfortunately not. For wiring centre I was meaning the big junction box below the cylinder stat.

The cylinder, stat and big junction box are in a cupboard upstairs whilst the programmer is below the boiler in the kitchen downstairs.

Understood.

I think you have a problem which will only be sorted by someone present on site.

So it seems there is no link between Terminal 1 at the programmer downstairs and Valve Grey/C2 upstairs. Its either never been done or is wired incorrectly to another terminal.

Yes, there is a missing link. Can't see how it can be wired to the wrong terminal. The Potterton PWB1 wiring centre is not helping as there is a PCB behind the terminals, so it's not easy to know how the terminals are connected together. A standard 10 terminal wiring centre is much easier to fault find.

Anything else I can do or look at or is there any possible work around?

Not easy. It would mean tracing each cable/wire and finding what each end is connected to. It might then be possible to work out a revised wiring scheme.