Potterton Prima turning on and off

[Ric2013]

Sorry, old chap. I had mistakenly thought you had a fanned Prima model!

You'll find a lot of old manuals on the Plumbase website. Potterton Prima Range - https://www.plumbase.co.uk/potterton-prima-range-10000851-0000 and scroll down.

You can probably help your RGI out by printing him out the manual for the boiler and leaving it to hand. Scroll down on this page and you'll see there are Prima B,C, and F ranges. I think only the F range is fanned and that it is the only one to have a circuit board and I (now) don't think that is what you have.

I don't really have the time to do more than scan through them quickly, but I'm guessing yours has no fan and has a permanent pilot light which you have to light manually and so probably doesn't have an electronic control (circuit board)? The only way to be sure is to find the GC number for your boiler (normally on a kind of aluminium label) as this will tell you the exact model and you can compare that to page 2 on the manuals.

Be aware the front casing forms a part of the combustion air circuit. You're in dubious legal territory (though I can't see the Health and Safety at Work Act being applied to you). If you're going to let curiosity get the better of you, I hope you'll be taking care not to damage the seal and to make sure that casing goes back on correctly and that the rubber seal is in good order. I trust you have a carbon monoxide alarm in the room?

 

[Gasinspect]

sounds like faulty pump overrun thermostat

 

[Ric2013]

sounds like faulty pump overrun thermostat

Would that cause the boiler to fire?

 

[Gasinspect]

Would that cause the boiler to fire?

Ah! good point, sorry missed that symptom. and does not have frost stat, and assume Hive doesnt either. Boilers with frost stats, guy at Potterton technical helpline once just said to disconnect it to stop random firing.

 

[West Country]

Thank you guys and thank you Ric2013 for you concern for my welfare . I'm very careful when ever I do anything with the boiler and I do have a carbon monoxide alarm, if it makes you feel better I'm an aircraft engineer.

So I've had a look at the manual and I can see why the pump overrun thermostat was mentioned it's the only thing with a permanent live. See wiring diagram below. I might be clutching at straws but could the overrun stat breakdown and provide a live back down the brown wire?

 

[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.