CH pump runs continuously, but ...

Just noticed that my CH pump is running continuously and that the house is getting very hot :-(
Having Googled, FAQ'd, and looked in here, I suspect that I might have 2 faults :-(
Installation: Potterton EP2000 (the old brown one), anonymous beige wall stat, Grundfos Super Selctric pump, Potterton Prima.
Due to unusual occupancy patterns, we've always run the timer on '24 hours' for both CH and HW and just set the temperataure on the wall stat and boiler stat (Yes, I know we don't need a timer, but it was here when we moved in!). This always worked fine. Boiler cycles, pump cycles.
As of today (maybe since yesterday) the boiler is still cycling as usual, but the CH pump is running continuously, and it's getting hot in here!
Thinking that the wall stat had gone short (despite it 'clicking' in a sensible place on the dial), I turned the EP2000 to 'off' on both HW and CH. But the pump still runs. I'd assumed that the wall stat was in series with the ouput from the EP2000, so if it had gone short that turning the output off would kill the pump. Apparently not :-(
The EP2000 has always had a flickering display (not a problem, we don't use it as a timer) and I've just checked the battery and it's dead, but I assume that's just to back up the clock in the event of power failure.
So to me it looks like the EP2000 is faulty (and may always have been) as 'off' doesn't seem to do anything, and that now that wall stat has gone short.
Does this sound sensible? I don't really want to replace the EP2000 if the stat is faulty, and vice-versa. Also, I'm not sure if the newer EP2000 is compatible with the backplate of my older one (any ideas?).
I don't know if there's a frost stat anywhere - I've never been able to figure out the wiring in this much-extended/much-bodged house.
Ideas?
Cheers,
Al.
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It could be the three port valve that is sticking... If you remove the timer from its back plate, does the pump still run?
Sparks...
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Yes it does! I hadn't thought of trying that.
So ... where do I find the three port valve and what does it look like?
And when I find it, what do I do to/with it ;-)
Cheers,
Al.
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The look like this (not always blue though!) http://www.screwfix.com/app/sfd/cat/pro.jsp?idS314&ts 786
You may not have one, you may have two single port valves, or just one - it depends on the install.
The pump will be connected to this valve (usually via a wiring box), so it is usually near that.
As for what to do with it - find it, then report back with model numbers etc!
Sparks...
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Looks like 2 single port valves:
"Appliance Components Limited Morortrol"
I'm struggling to understand how a failed valve is causing this problem, but then again, I don't do plumbing ;-)
Thanks for the help so far,
Cheers,
Al.     
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Okay, here is how it works....
Your timer has two circuits, one for the Central Heating (CH) and one for the Hot Water (HW) Live goes into this timer, and when the timer decides you want CH or HW it applies that live to the appropriate terminal (one for CH and one for HW)
You also have two electric valves - one valve controls water to your HW cylinder and the other to your Radiators.
Both these valves are connected to the relevant terminal on the timer via a thermostat (room stat for the CH and cylinder stat for the HW) so when the timer AND the stat are BOTH asking for heat, the valve operates.
Now, so we don't end up with a closed valves and the pump on, the pump (and the boiler) are connected to a little switch in the valves (in parallel, so when either valve is operated, the pump and the boiler are turned on)
It sounds like one of the valves has stuck open, causing the pump and boiler (The boiler will still cut in and out as it has it's own internal thermostat so it only fires when the water temperature is too low) to stay on even after the timer is not calling for heat (removing this from the wall proves it is not the timer sticking on)
Now we need to find out what valve is causing the problem here. I suggest you remove the timer from the wall again and leave it off for 30 minutes or so - this will remove the power from both valves so they should both be off. After the 30 odd minutes, go and feel the pipes both sides of the valves - the one that is sticking on will be hot both sides, whereas the one that has shut off will be cooler.
If you can't see what valve is for what, then find your hot water cylinder and feel the pipes going into the SIDE of this and see if they are hot.
You did say earlier "The CH pump is running continuously, and it's getting hot in here!" witch does indicate it is the valve connected to the CH side - But it doesn't do any harm just to check!
Let us know your findings!
Sparks...
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[snip]
Thanks - Makes sense now :-)
It turns out that the HW valve is permanently open. After cleaning the exteriors of the valves up it looks like the HW is switched to the open position (there's a little slider on the end of the valve). It's not clear from the markings which is the open position, but the two valves are set to opposite settings.
So I guess that explains why the pump runs continuously. I think the heating 'problem' yesterday was a red herring - We had a house full of people, all of the lights on etc. When the pump kept running I assumed it was a CH problem :-)
Is there any reason why the HW valve should be set differently?
BTW, the house used to be a bungalow (now extened upwards and outwards), so the HW cylinder and boiler are both on the ground floor - I guess that's why it's a fully pumped system.

Good job that I did!
Cheers,
Al.
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Simple really isn't it :-)

If it is the same make and model as the CH valve, then no (assuming the power was removed from it of course)
One last think I would suggest is to turn off the power to the heating system completley (normally via a Fused Connection Unit (FCU) near the boiler) this should stop the pump and make sure there isn't any power going to the valve keeping it open (maybe even turn off all the power in the house to be 100% sure someone hasnt crossed wired it somehow!)
If this still keeps the valve open and it is exactly the same make and model as the CH one then I would say it is faulty.
Now these valves work with a little motor and a spring - when there is power applied to the valve it opens, then when it is removed, the spring pulls the valve closed again. The spring may have broken or come loose, but more likley, the actual valve that rotates (just like a 1/4 turn tap) is sticking for some reason.
You say there is a little leaver on the side - when everything is off from the boilers FCU (pump not running!) try to manually move the lever, but don't force it and break it! Sometimes they stick because they have been on permanantly for weeks on end (normally because you have the HW on 24h on the timer, and the thermostat on the side of the cylinder is set to high (too high meaning higher than the boilers internal stat) sometimes they can be jiggled and then they are fine - I would suggest trying this before you change it.

Sounds logical to me!
Sparks...
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I'll try it. I think everyone here is getting fed up with my 'experiments' with the CH and HW at the moment, so it will have to wait a while ;-)

Yes. It looks like a lever rather than a position indicator because there's a sort of 'gate' arrangement to latch the lever into. Interestingly, it's not latched, but just back in the what I assume to be 'open' position. So I don't know if this has been manually set that way or is just indicating the the valve is open. Sadly t'internet reveals little of these Canadian-made valves, so no data sheet to check.

Sounds like a job for Monday morning. I don't move little breakable levers on Friday evenings ;-)

Interesting. We do run the HW and CH on 24hrs. I'll see if I can determine the relative settings of the boiler and cylinder stats.
Cheers,
Al.
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In an earlier contribution to this discussion,

A possibility which no-one else seems to have mentioned is that the pump may be controlled by the boiler - and not directly by the timer/3-port valve etc. Many boilers *do* control the pump in order to keep it running for a while after they stop firing, to prevent overheating due to the residual heat in the heat exchanger.
If the boiler does do this, and if the thermostat within the boiler which provides this function fails shut, the pump *will* run continuously - regardless of virtually every other component, short of turning everything off at the FCU.
--
Cheers,
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Could be. I think it's an overridden/failed valve at the moment, but I'll see if I can figure out if the boiler is in control.
Cheers,
Al.
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