Central Heating Only Operates With Hot Water

[Aberlake]

Hi,
Got a very strange problem that maybe someone can help me diagnose. Heating system is an open type with a Potterton MP3 motorised valve, Potterton EP3000 programmer and Potterton stat. Central heating only activates and runs when water is heating. If water only is selected then only water heats, but if heating only is selected then nothing happens (system appears to energise, stat lights up but boiler doesn't fire and pump doesn't run) If I select both heating and water then boiler fires and both run, but as soon as water hits temperature the heating goes off as well!

Initially I blamed motorised valve but if this was faulty surely heating wouldn't work at all? Could it be a controller problem (loose / broken wires?).

Any help / advice gratefully accepted.

Richard

 

[ChrisR]

Motorised head fault. There's a separate microswitch inside for "CH only".

 

[Aberlake]

So all I have to do is replace the motor pack then? That's great as it seems I can get one for around £20 locally. I take it that the microswitch also enables the boiler to fire? Is it practical / possible to replace the microswitch?

Thanks for the speedy reply - greatly appreciated.

Richard

 

[nickso]

So all I have to do is replace the motor pack then? That's great as it seems I can get one for around £20 locally. I take it that the microswitch also enables the boiler to fire? Is it practical / possible to replace the microswitch?

Thanks for the speedy reply - greatly appreciated.

Richard

some have stupid screws that you cant get out easily....just replace the whole head at that price.....in fact buy two cos you will have to do it again soon anyway.

 

[JohnD]

An even more cheap solution:

Have the HW on.

Some systems were built like that.

Assuming your cylinder is properly insulated and has a working cylinder thermostat it is not going to draw heat away from the Heating once it is up to temp (about 20mins from cold).

 

[nickso]

An even more cheap solution:

Have the HW on.

Some systems were built like that.

Assuming your cylinder is properly insulated and has a working cylinder thermostat it is not going to draw heat away from the Heating once it is up to temp (about 20mins from cold).

thats the point though.....when the cylinder reaches temp the heating goes off. new valve required or repaired if you can get into it.

 

[MANDATE]

Same problem couple of years ago. Its not practical to replace microswitch. Myson actuator heads are the replacement for potterton.
Look up the myson site. New head I think was £40.
If the valve is not moving fully across then problem may just be the motor. New head will of course cover both.