Bizarre central heating problem

Right, my central heating system consists of a Potterton Suprima 30 balance flue boiler and EP2000 programmer, with a Myson MPE322 3-port valve and a Myson compact CP35 pump.
All was fine until yesterday, however now the boiler refuses to fire up when it's supposed to come on and the pump just seems to run continuously, even when the heating/water isn't programmed to be on.
The only way to stop it is to turn the power off to the system at the fused spur plate, otherwise the pump will just continue pumping cold water round the system.
Any suggestions? I did have a similar problem about 2 years ago, which I was told was probably due to the 3 port valve head (which also kept jamming itself onto either heating or DHW and required you to flip the ports override switch to get it to move). I changed the head and all seemed well, but now the system has started playing up again, though the head hasn;t been jamming like before.
Could it be the 3-port valve head again, or perhaps something to do with the boiler or programmer?
Thanks in advance, hope I've not left anything off the description (I'm quite handy with a screwdriver, but plumbing and heating is not exactly my forte).
--
Best Wishes
Simon Taylor
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Simon (Dark Angel) wrote:

To paraphrase Bridget Jones, you had me at "Potterton". ;-)
There's been heaps of discussion about Potterton Suprima boilers (here's a typical thread from a web forum http://www.howtomendit.com/answers.php?idc114 ) . I'm sure you can google for plenty more on uk.d-i-y. A lot of dodgy PCBs that Potterton have been replacing free in the past (dunno if this is still the case for your boiler)
User guide here. http://www.potterton.co.uk/docs/Potterton_Suprima_HE_User_Guide.pdf
HTH
Tim
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On Mar 12, 12:27 pm, "Simon \(Dark Angel\)"

I'd guess its' the value. I think the pump is typically controlled by the a inside the motorised value so it comes on when the value is actually open, whether or not the valve is supposed to be open. If it's stuck open the pump will run continuously. But I don't know why the boielr does not fire as well. perhaps it's cleverer than that.
Robert
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Sorry: I meant...
I'd guess it's the valve. I think the pump is typically controlled by a switch inside the motorised value so it comes on when the valve is actually open, whether or not the valve is supposed to be open. If it's stuck open the pump will run continuously. But I don't know why the boiler does not fire as well. Robert
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In an earlier contribution to this discussion,

No, this is *not* a problem with the valve. Under some - but not all - circumstances the valve tells the boiler to fire. The pump is either wired in parallel with the boiler, or controlled by the boiler - in cases where pump over-run is required.
The valve *never* tells the pump to run without firing the boiler. The problem is in the boiler itself - which is being told to fire but isn't doing so. As others have said, the PCB in this particular boiler is a frequent cause of failure - so is probably the first place to look.
--
Cheers,
Roger
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Exactly
boilers are not something where people who don't actually know the boiler in question should make guesses based on their (different) system
The pump relay on the pcb is controlled by a microcontroller, The only controlling inputs to the pcb are switched live and temperature sensor
If the pcb goes into lockout (a common problem), the pump relay is continuously activated as a safety function
it's the 'kin pcb
--
geoff

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On Thu, 12 Mar 2009 12:27:31 +0000, Simon \(Dark Angel\) wrote:

The normal operation would be for the pump to run for a few seconds and then stop. If there is a heating demand then the pump will run. Ergo the problem is in the boiler it might be the PCB (balance of odds it is) or it could be something like fan. More info , what lights are on.
Is the fan running?
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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Hardly bizarre - its one of the standard pcb faults
I presume that the red light is flashing too
As Ed Sirett said, its the only boiler where you change the pcb then look to see if there are any other faults
--
geoff

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writes

Well said Maxie. The best thing he can do is:
1. Drain down, 2. Remove boiler off the wall, 3. Take into the garden 4. Attack boiler with a sledge hammer. 5, Buy new proper boiler like a Broag.
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On Thu, 12 Mar 2009 21:23:37 +0000, Doctor Drivel wrote:

I shall have to save this as one of the few posts where I come close to agreeing with Dr D. ;-)
However my own procedure is:
1. suck teeth 2. say Oh Dear That'll Cost Yer 3. get a properly fixed PCB cheap from Geoff 4. fit it and charge customer an arm and a leg 5. blame Potterton
--
John Stumbles -- http://yaph.co.uk

Who's *really* behind all these conspiracy theories?
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Yes it was, but the reset button failed to do any good.
However, I still had the OLD 3 port valve head kicking around, so swapped it back and now the system seems to be working again (for the time being anway).
Incidentally, I did get a reconditioned board from someone advertising on this very newsgroup about 3-4 years ago, so I hope it's not that that's gone wrong.
--
Best Wishes
Simon Taylor
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Strange, the pcb has no direct interface with the 3 port valve

That would have been me
--
geoff

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Co-incidence maybe? I'll swap them back again tomorow and see what happens.

Oh well, might be ordering another one from you in the not too distant future.
--
Best Wishes
Simon (aka Dark Angel)
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My daughter has a Potterton EP2002 system with a Potterton Suprima 40L boiler and a MPE322 diverter valve. The system seems to be working OK for hot water but has developed a fault with the CH. The CH will not come on unless the HW is on and the radiators will only heat up for as long as it takes for the water tank to reach temperature. When the tank stat says enough, the system stops heating, no matter that the room stat is still calling for heat. I have remove the diverter actuator and checked that it moves according to demand. The valve is free to turn by hand. The boiler fires when hot water is required (green light on) but will not fire for CH only (red light on). We did get it to fire for CH only by returning both controller sliders to 'off', switching the system off, then switching it on and sliding the CH control to 'on'. The boiler fired for a few seconds then shut off again. Can anyone point me in the right direction to get this fixed? Thanks.
url:http://myreader.co.uk/msg/1391142635.aspx
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My first guess would be the microswitch which should operate at full travel (CH only) of the mid-position valve is not actually operating. Maybe because it's faulty, or maybe because the actuator isn't moving far enough to operate it.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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In an earlier contribution to this discussion,

I assume from the fact that it is capable of heating the CH and the HW at the same time that it is a Y-Plan system - so that the 3-port valve is a mid-position jobby and not a simple diverter valve, as used by W-Plan systems. Is that right?
If so, the problem is pretty certainly associated with the valve. My first thoughts were that the 'wet' part of the valve was seized in the mid-position - preventing the actuator from moving far enough to be able to switch the boiler on in CH mode. But you say that the valve is free, so it can't be that!
The next most likely cause is that one of the microswitches in the actuator has failed. In HW-only and HW+CH modes, the boiler is driven by the cylinder stat. But once the HW demand is satisfied, the valve moves to the CH-only position, and relies on one of its internal microswitches to switch the boiler on. If the micro-switch fails to make, you get the problem you describe.
*But*, there's one more possibility. The cylinder stat is a change-over switch and, when the demand is satisfied, it provides a live 'HW satisfied' feed to the actuator - without which the actuator can't switch the boiler on. If the change-over contact on the cyl stat fails, you will also get your symptoms. The way to check it is to turn the HW off at the programmer - causing the programmer to provide a 'HW not required' live feed to the actuator, which does the same as the 'HW satisfied' feed from the cyl stat.
If the CH heating works ok with HW switched off at the programmer, the problem is in the cyl stat (or its wiring). If it doesn't, the problem is in the actuator - which needs to be replaced (or repaired - you like fiddly jobs!).
--
Cheers,
Roger
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For once someone has a problem with a Suprima which is not pcb related
The boiler doesn't know whether it is heating for DHW or CH, so that's not where to look
The fact that it actually reacts to the programmer would indicate that the relays in the programmer are OK
This leaves the diverter valve - I would suspect that you have a problem with the microswitches, they can melt the case or the contacts can weld themselves together
--
geoff

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On Mon, 4 Jan 2010 04:34:10 +0800, "David

Now I know your boiler is not the same make as mine (Baxi), but the symptons are the same when I had your problem. I understand it was a small "circuit board" that sensed (or was supposed to) if the gas was was flowing. Tap water .. no probs but when CH selected, it ran for 10 secs and shut down. It was an intermittant fault, but changing the board sorted it.
Mike P
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Sorry - completely irrelevant
--
geoff

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In an earlier contribution to this discussion,

I don't think that's the same thing at all! I assume that you have a combi boiler - which provides 'instant' hot water *or* central heating, but not both at the same time? This uses internal sensors to select the desired function.
The OP has *stored* HW and *external* controls to direct the boiler's output to the HW circuit or CH circuit or both. The boiler itself neither knows - nor cares - which it is heating at any given moment. The OP's problem is in the external controls, *not* in the boiler.
--
Cheers,
Roger
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