Potterton Performa 28i DHW but no CH

[ppb39690]

Boiler makes no response to call for CH. Have eliminated timer and thermostat by unplugging timer and linking across thermostat circuit terminals.
The CH neon never illuminates, nor does any fault register with the system. It seems the PCB is not seeing the demand for CH.
HW is working fine. System was running with low pressure when fault occurred. Now repressurised to normal operating range.

Reviewed various threads and symptoms seems to point to either the diverter valve or PCB. How can I work out which or if either is at fault? Would the CH neon come on if the valve was the problem?

 

[baxpoti]

Have eliminated timer and thermostat by unplugging timer and linking across thermostat circuit terminals.

If you a built in timer and have unplugged it, as opposed to linking it across, the boiler will still not have a demand for c/h!

 

[ppb39690]

Timer is 'optional' according to manual and I assumed that removing the plug would not break the circuit. I'll have a go at connecting across it instead.[/quote]

 

[baxpoti]

Connect the two black wires.

Be aware 230v!

 

[ppb39690]

Reattached timer and linked black wires. Still no joy.

 

[Agile]

You will need to test with a meter to see where the call for heat voltage has gone.

Tony

 

[baxpoti]

With selector switch in heating and hot water what lights are showing?

1. With hot tap on preheat off

2. With hot tap off preheat off

3. With preheat on

 

[ppb39690]

Had another go and ...
After waggling of some of the PCB wiring the Central Heating came on for about 15 secs and then turned off.
Had another go removing and reconnecting the connections to the PCB and still off.
Disconnected the two microswitches and checked nipples were out and that the switches operated manually. This seemed to clear a block somehow and the CH call light came on.
However, when the DHW preheat was turned up the CH went off as expected but did not restart when preheat turned back down. The Ch would not start unless the DHW was on. However, this seems to have cleared as system is now starting up with a call from the thermostat with the DHW off. Still doesn't like the DHW preheat being turned on though but as I don't use this function normally I can live with it.

Seems that at the moment with the DHW preheat on low/off and CH med/high the system will work. Still not sure what was at fault or if it'll occur again but at least I have heat for now!