The CH only works when the HW is on - help!

6 Jan 2009
Reaction score
United Kingdom
I have a Potterton Netaheat boiler and Potterton Ep2000 controller.

The Central Heating won't work on it's own - I've tried using the timers, 24 hrs and over-ride function. I can hear the thermostat click when I hit any of these functions but nothing happens.

However, if I set the HW to 'once' or 'twice' or 24hrs and then put the CH to the same setting, the boiler fires up and I have heat.

I can't seem to control the temperature using the thermostat.

Since this problem started, my work-around used to work if I pressed the 'over-ride' HW button and then the 'over-ride' CH button. However, I have noticed that the 'over-ride' function no longer works for either CH or HW.

The diverter valve appears to be moving as follows:
From turned off to HW on, the valve moves and HW's on
From Turned off to CH on, the valve moves but no CH
From turned off to CH/HW, the valve moves and we have both.

Can anyone help?!
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Valve head sounds faulty. Microswitch broken and not telling the ch to come on.
I have had a plummer out who took the motorised valve off and said it appeared okay. What trade is best skilled to fix this?

One thing I forgot to mention, before this problem arose, everytime the hot water came on the valve made a ticking noise. It doesn't anymore!

Out of interest am I doing my heating system or boiler any harm using my work around of having the hot water on to get heat?

I really appreciate your help :)
Normally a heating engineer would swap this.

No you won't do any harm to your system, but with the valve in mid-position manually, your hw will get very hot, so be careful when using the hot taps etc.
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Aaaagh! That explains why the water's steaming hot even to my dish-pan hands!

You've been really helpful, do you have a twin in Hampshire I could call?!
I have checked the movement of the diverter valve and it does move to the CH , HW and CH/HW part. Could it still be faulty?

Out of interest, is this something that I can replace myself? Am I likely to get into any trouble, with leaks etc if I do it?!

Where I have lost the 'over-drive' function on the Potterton EP2000 box, is there any chance the problem could be here?

Pushing the valve right over to the CH position will correctly send the water through the radiators but if the microswitch is broken the voltage that tells the boiler to fire up wont be sent out.

Many valves have replaceable heads so no plumbing is required but a certain amount of wiring is necessary and the head carries mains voltages.
Thanks for explaining this.

My boiler has been 'kettling' a bit and today it sounds as if I am running a tap. could this be where I have had the HW on to run the central heating?


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