CH problem - Help Please!

[steelee]

Hi, sorry if I sound confused but am a novice at this! Have a problem with CH in that it only seems to work while the HW is on, if I turn HW off at the programmer then the boiler cuts out and only comes back on when I turn HW back on (then not all the time as I think that if the HW is up to temp the boiler isn’t cutting in)
This has only started happening in the last few days but had a similar problem a couple of years ago and called in a plumber in who replaced in this order...2 sensors in the boiler (no joy) the pump in airing cupboard (no joy) the myson 3 way valve (no joy) finally the pcb board in the boiler (working)
Don’t really want to go through all that again as it took over a week to sort and have a 2 month baby in the house now so could do with some heat....system is a Potterton Supr1ma boiler, EP3002 programmer and Myson MPE322 3 way valve, I assume the pump is working as 1 I can hear it and 2 HW is working fine, therefore I am thinking that either the programmer or 3 way valve is at fault, would this be reasonable to assume and which should I replace first?........Lights on valve are working correctly in such that they correspond to whatever the programme is set to (HW or CH or both) but as said only getting CH when HW is on and then not every time, would it also be reasonable to expect it to go more than a couple of years without failing.....again!!.
Any advice would be very welcome......
Cheers

 

[gavinda]

does the heating work if hw is on at the clock and off at the hw cylinder thermostat?

 

[steelee]

Have turned thermostat on tank to 0 but CH not kicked in, so no it does not seem to.

 

[gavinda]

in that case.. can you check the voltage to your 3 way valve. you should have ~240v ac on the white wire and the same on the grey wire when ch demand only.

 

[steelee]

Gavinda, thanks really appreciate your advice but I don’t have a volt meter as this is not my thing really, When I turn the thermostat on the tank to 0 the HW light on the 3 way valve goes out, CH light stays on but boiler dosn’t fire up, as the valve is only about £40 would it be worth just replacing it before going to the expense of calling someone in as I am ok with wiring a new one in?
Cheers

 

[gavinda]

it MAY be. you should maybe also remove the actuator and check that the valve body spindle is free and easy to turn. if its not the i would recommend replacing thew whole valve. not to say the head wont do it, but if the body is getting sticky, you're just covering up the real prob.

 

[steelee]

Ok and thanks for your help.

 

[steelee]

Also as an intrim thing to get some heat into the house could I move the valve from auto to mid, would this work or is that for something totally different?

Cheers

 

[gavinda]

thats whats happening anyway mate... its motoring to mid and just on when hc stat calls. once its satified you're back to square 1

 

[gavinda]

thats whats happening anyway mate... its motoring to mid and just on when hc stat calls. once its satified you're back to square 1

 

[MANDATE]

thats whats happening anyway mate... its motoring to mid and just on when hc stat calls. once its satified you're back to square 1

So are you saying there's no way to cheat the sysytem and get some heating?

 

[Tipper]

Roomstat not calling for heat?

 

[MANDATE]

He does get some heat , but only with HW so can't be room stat.
Either the valve does not go beyond midpoint (faulty motor/no power on grey wire) or tight spindle, or if it does then faulty micro switch.

 

[gavinda]

thats whats happening anyway mate... its motoring to mid and just on when hc stat calls. once its satified you're back to square 1

So are you saying there's no way to cheat the sysytem and get some heating?

dont think so. got a cheat you can share? it'd help me get out of tight spots this winter.