Potterton Prima turning on and off

[Ric2013]

To be fair, you seemed to know what you are doing, but I'd rather state the obvious than have you gas yourself... before we find out what the problem is anyway But then I'm assuming you also have a volt meter then, which means you could connect it to the switched live (you might be able to use the 'test socket' terminals on the boiler) and will make a diagnosis easier.

I'm clutching at straws too, but we're thinking along similar lines. The pump is switched by the boiler and the over-run stat could power it with the system controls not feeding the switched live. But that wouldn't explain it if the gas valve is also opening. Unless somehow we have 1,2, and 3 all connected together somehow.

I suppose at this point I'd want to confirm whether, during this weird erratic behaviour, the pump is receiving power, whether the boiler is firing, and whether the gas valve is receiving power as certain hypotheses could then be ruled out. I find that sometimes in these situations, careful observation reveals it all should have been obvious all along.

 

[West Country]

So I'm away this week so can't do anything with the boiler. Here is what is happening the Hive has lights on it showing when either HW or CH is on, I'm happy that there isn't a spurious signal from the controller as it was the same problem with the old switch master. The problem occurs when the heating is off and no lights on the Hive.

The pump runs when j gets the problem and continues to run for a short period. I assume that is normal behavior for the pump to run on.

The boiler sometimes fires up so I'm assuming the gas valve opens. Sometimes it's momentarily sometimes for 30 seconds or so.

Now I think about it, I think it only does it after the boiler has been running (intentionality). I'm not 100% sure but it would fit with the pump overrun stat.

I was thinking of disconnecting the inputs from the hive and leaving only the permanent live to prove 100% it's an internal fault. I'm also thinking of getting my multimeter out and doing as you suggest. I am tempted to just change the overrun stat, I don't think they are much.

Please carry on stating the obvious

 

[West Country]

I've had someone round and I have the answer. It was the pump overrun stat, it's broken down internally (you can hear it rattle) and was providing a feed to fire the boiler.