Potterton 30 F question

[uk_dilbert]

Afternoon Folks,

In the past month I've noticed the boiler cutting out after approx half and hour. When you fire it from cold everything happens in sequence, fan, air pressure switch, gas valves, spark, ignition etc but then after 20-30 mins the system turns itself off entirely. If you start it from cold it takes a couple of minutes to boot up but ignites again, only to shut down between 5 and 10 minutes later. The third and subsequent times it won't ignite at all, fan comes on but thats about all.

I had a it serviced a few days ago and the engineer said the problem was the gas valve (apparently a common issue on this model), when he started it up it was exactly the same as so the problem became the air pressure switch which he fitted too with exactly the same result., he also stated that it could be the pcb.

I'm getting the feeling that he is clutching at straws so did a bit of investigating myself. I noticed that each time you cycle the power and turn up the front thermostat knob, you don't get any activity until you get to 3 , 5 or even max sometimes.

Any ideas? i don't have any experience in the area but it seems to be something to do with a thermostat or something cutting out on the boiler but I don't quite understand why as the radiators are not that hot.

Any help greatly appreciated as I'm a bit confused

 

[Rob]

Your post is a bit confusing. Firstly is the boiler model a profile or prima etc?

OK firstlt the front knob is just a stat connected to a microswitch. If the boiler doesnt kick in untill MAX then it means the boiler is already very hot and you may have a circulation problem in the system.

However once the fan is running then the boiler should fire up. You need to then measure APS contacts then finally if the gas valve is getting power.

Does the fan just run continuous or cycle on off?

 

[ChrisR]

I'm getting the feeling that he is clutching at straws

Me too!
COuld be thermostat, or as rob says , circln due to sludge or tired pump.

 

[uk_dilbert]

Thanks for the replies.

Rob, its a prima, apologies for the confusing post but I've been trying to work out the whole thing in my head and its driving me round the bend.

When the system is on the fan runs continuously until the threshold is reached then everything turns off.

If its the circulation system, is there a guide or website which will show me what initial diagnostics I can do before calling anyone in?

Cheers for the help so far