Grundfos Alhpa & Potterton Suprima 'bug'?

I would hazard a guess that the boiler is controlling the pump, and that it has a pump over-run stat to stop the boiler from overheating.

If this is the case, the pump will run when either or both of two conditions are satisfied: a) the boiler is receiving an "I want heat" demand from the CH and/or HW system, b) the boiler outlet temperature is above the over-run stat setting.

So you get the following scenario: The boiler is firing and the pump is running. The room (or cylinder) stat (but *not* the boiler stat) opens. The boiler and pump stop. The residual heat in the metal parts of the boiler's heat exhanger continues to heat the water to the point where the over-run stat switches on (maybe several seconds after the boiler has stopped firing). The pump starts up again in order to carry the residual heat away from the boiler.

If this is what you're experiencing, it's quite normal.

In message , Set Square writes

Well not a stat, it's software controlled and pump overrun in a Suprima is 20 minutes

As I explained when he posted this question the first time, the pump is pulsed at the beginning of a heating cycle

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Sorry about the double post - I've just started using Thunderbird and thought I'd deleted this message. I've followed on to the earlier post, but one additional point is that my (4yr old) Suprima overrun is only 2 mins (I've timed it a few times).

Maxie always does things x 10.

Strange, this can only be a software timing thing and if everything else is working, I don't see how something like that can happen

In message , IMM writes

It's normally what I have to count up to when reading your posts ..