Netaheat boiler

[KenL]

I have a Potterton Netaheat Profile 60e. It worked fine until last week. Now it has developed a delay between the fan starting and the boiler firing up. This delay varies between 10 minutes to over an hour. The funny thing is that it starts up ok first thing in the morning until it reaches the heat and the roomstat turns it off. When the roomstat turns it on again the delay sets in. I've checked the CH pump and the roomstat and both work ok. It was particularly windy last week, could this have damaged the air pressure sensor, or is it a boiler thermostat problem?

[Brian Reay]

If this beast works as I recall, there is a sealed cover that the fan pressurises before the burner fires, the pressure being sensed by the pressure sensor.

One possible problem is a small leak - so the fan takes longer to get the pressure up. The difference in "first time" and when the system has been on earlier could be a simple issue of the leak being sealed when cold and opening when warm.

Brian

[Ed Sirett]

If there is a leak in the combustion chamber cover then that is classed as a serious safety fault.

More likely there is debris at or around the inlet to the pressure tubes or the APS is marginal.

However the delay could be coming from the time between pilot ignition and full gas. This could be due to a failing gas valve sensor bulb or more likely a dirty pilot flame that's not heating the sensor aright.

The OP should make sure the boiler is serviced based on a thorough strip down. Then see what symptoms still remain.

[KenL]

Thanks for your replies ...

Brian, Ed ... The leak theory, sounds expensive and potentially dangerous. In view of that I have arranged for an engineer to call on Saturday.

Geoff ... The fan runs and runs then eventually when the ignition spark clicks it lights immediately. I've checked the flue outside and there is no smell of gas.

[Brian Reay]

Good idea- not something to tackle yourself but good to have an idea on what is happening.

Brian

[KenL]

All ... thanks for your help. The engineer called and serviced the boiler. He spent a bit of time on the air switch side and found that one of the tubes (into the flue) was suspect. All appears to work now.

Ken