Combi boiler wont fire up.

[terrybilly]

My Biasi combi boiler has stopped working,when you start it up it makes all the right noises as if is about to fire up then stops and the red light comes on for a few seconds then starts the process again. Any ideas?

[Caladon]

Check the water pressure gauge. Even when off it should not be zero but be quite high.

Combis slowly lose water pressure over time so there is a valve underneath it which allows you to increase the pressure within the enclosed system.
If the pressure is too low then it stops completely.

[Hymie]

What model is it � this information will help others in diagnosing the problem.

I doubt the problem is low system pressure, normally a boiler will indicate this condition (by fault code or lamp), and will not start any ignition sequence.

Given the time of year, I take it that the fault occurs when you turn on a hot tap � does the same happen if you switch on the central heating?

[Hymie]

Although many faults could cause the effects you describe, my best guess would be that the pressure switch is not operating for some reason.

When a combi boiler �fires up�, it switches on the fan to exhaust the burnt gases � to ensure the fan is operating, the boiler senses the pressure drop (causing the air to flow). If the pressure switch does not sense the required pressure differential, then the boiler will not supply gas to the main burner (and will shut down).

This could be due to a faulty fan, perished tubing to the pressure switch, air leaks within the boiler, a faulty control board, loose wiring, faulty pressure switch and more.

Best call in an engineer to fix it.