Potterton Performa 24 Cycling

[arran197]

Weird one this, above boiler, comes on and stays on. Once it starts to get warm, it goes off, then a couple of seconds later, fires up again. Then after about 15 seconds, it goes off and starts again. No flame failure light. Boiler gets up to temperature.

I've checked the NTC, which is only a few months old. Working fine, 2 K when warm, increasing as it cools. Heat Team told me to check the return filter, clean as a whistle. Pump is only 6 months old and is working fine, all the rads get hot anyway.

One thing that is very strange, the DHW temp control knob controls the heating. Turn it down, boiler goes off, turn it up and boiler come on. The CH temp control doesn't appear to do anything.

I'm leading towards PCB, but I'm confused as to what's going on really. PCB isn't that old either, date on it is 06/12. Wondering if it could be the wrong PCB?

Any help?

 

[moogwai]

Have you checked the probes, might bending towards the burner when hot and not recognising the flame. Just a thought.....had a similar problem with a cycling glow worm betacom c.

 

[Ollieg]

Does it have Pre Heat?

 

[arran197]

No, I don't think it's got pre heat. I don't think it's a rectification issue, it fires for too long and doesn't throw a fault light. What I don't understand is the temp control knobs.

 

[Ollieg]

Sometimes people swap NTC leads over for testing. Maybe this is the problem.

 

[arran197]

I don't think there is an NTC for the DHW and even so, on CH mode it shouldn't matter if I turn the DHW, that would imply the potentiometers are reversed. The thought did cross my mind though.

 

[Ollieg]

Yeah your right.
My brain is mush.

 

[Ollieg]

I have had a few things do this.
PCB fault.
High and low burner pressures set wrong. Causing little or no modulation.
Loose plugs on pcb

 

[gasfun]

Had the same problem a while ago. It was the dhw pressure diff valve that was clogged up with dirt. Restricted the diaphragm. That shut the boiler off every 14 seconds.

 

[arran197]

I went back today and fitted a board, did the same. Heat Team tech said change the DHW flow switch. He reckons it's sticking, but I'm not sure myself.

Might have to look at the valve. Did you just take off the differential valve or the whole manifold?

What is most weird is that the DHW temp knob controls the CH temp.