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By FrustratedJoe

Could anyone take a guess at what might be causing my Potterton Promax 24 HE to keep starting, running a bit, then stopping, then rinse-repeat ?

A little more for you on the setup - 3 channel central heating (2 heating circuits, 1 hot water), 2 thermostats for the heating, an upstairs one and downstairs. Both Potterton PRT2's.

When both thermostats are calling (and hot water circuit is off), the system fires fine and keeps running. But when the downstairs thermostat stops calling the above cycle starts.

I've tried swapping the thermostats front plates around to check it's not the thermostats themselves, but always happens when upstairs is off, and downstairs is on, regardless of the frontplate on the thermo. So figuring it's not the thermostats themselves.

Any ideas?
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no. its could be the thermostat setting on your boiler set too low. whats it on?
turn it to max and try it.
The temperature is set on the board, no control dial. Brand new board too (problem has existed before the replacement of this though). Doesn't explain why the boiler will on/off/on/off when only on 1 circuit though ... or are you suggesting that perhaps this single circuit is hot enough, thus boiler is simply responding to the temperature of the water in it? There is a way to increase the temperature of the boiler, single jumper. Increases it from 66C to 88C or something close.

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