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Andrew Smith
Andrew Smith, HVAC Technician
Category: HVAC
Satisfied Customers: 3591
Experience:  Heating and Controls engineer
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I have an Ideal Classic LXFF & FF Fanned Flue Gas Boiler that

Customer Question

I have an Ideal Classic LXFF & FF Fanned Flue Gas Boiler that provides us with hot water and central heating. It works very well and hasn't really given us any problems and we have it serviced every year. However, I recently have noticed that the boiler sometimes ignites of its own volition at times when it is not programmed to come on; it is only for about 20 seconds then switches-off. During this period the controller HW and CH lights do not come-on. I do have a gas servicing and fail safe contract with a local company and in an effort to solve the problem they have recently changed the motherboard in boiler; also I have replaced the controller (Danfoss). They say that the valves are all working correctly in the airing cupboard. Do you have any ideas? I'm now unsure whether it is actually a problem or whether it is behaving itself correctly.

Regards,

Andrew Folliard
Submitted: 3 years ago.
Category: HVAC
Expert:  Andrew Smith replied 3 years ago.

Andrew Smith :

When it tries to ignite, is the fan running?

JACUSTOMER-y0ha6e1p- :

Hi Andrew,

JACUSTOMER-y0ha6e1p- :

As far as I can tell before the boiler ignites of its own volition the fan is not running.

Andrew Smith :

ok, if the fan is not running then it is not an external control fault

Andrew Smith :

It may be a problem with the air pressure switch, if the wind blows into the boiler and it is a bit sensitive

Andrew Smith :

but it would need checking

JACUSTOMER-y0ha6e1p- :

Would the air pressure switch be in the flue or boiler?

Andrew Smith :

top of the boiler, next to the fan usually

JACUSTOMER-y0ha6e1p- :

Can you explain you explain the function of the air pressure switch and how it could be causing the problem?

Andrew Smith :

The air pressure switch detects air flown when the fan is running and tell the PCB via a pressure switch that it is running and proceed to the next stage of the ignition sequence.

Andrew Smith :

If the small gasket inside the air pressure switch is stretched slightly then the fan may not produce enough air pressure to keep the APS open all the time, this would make the flame drop out and go back through the ignition sequence, but the fan would be running constantly

JACUSTOMER-y0ha6e1p- :

I have checked plastic tubes that are attached to the APS and these looked to be alright, but the tube that vents atmospheric pressure from the fan may have been partially blocked, so I replaced the tube. The problem is till evident and te fan defintinety is on when alaced this tube.

JACUSTOMER-y0ha6e1p- :

I have checked the plastic tubing from the boiler to the APS and these all look to be alright. However, the tube that is connectes the boiler tp atmospherereappearwed t obe partially blokred s I have repalced this tube.d t he fan and spheris

JACUSTOMER-y0ha6e1p- :

Sorry about the second paragraph but meant to say that I am now looking to replace the APS.

Andrew Smith :

I think that would be the best thing to try first if the fan is running

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