I have a SIME Format 110C Combi boiler which uses a SIT 845 Sigma gas valve.
I've spent 2 weeks trying to isolate the problem with my boiler. It gradually ground to a halt, it began by only firing after a reset then it only came on in the evenings for a few hours.
The fault light I am getting is telling me it was the air pressure switch which i have tested, also tested the fan and the pump and I've changed the ignition transformer and the safety stat (after being told these were defintely the problem by a CORGI engineer)
I've tested the PCB and confirmed that it is sending the correct voltage to the safety stat and the gas valve.
Whilst changing the safety stat I accidently left the power on and something happened which fired the boiler. I decided to play about with the safety stat connection, when i fiddle with it on the start up sequence i can get it to fire the boiler, when the temperature in the rads reaches optimum level the burner shuts down (I am presuming this is because of the electrical modulation of the gas valve)
After a few seconds the boiler trys to fire again and it cannot do it so i get the fault light again. I can make it fire again by repeating the above procedure of disconnecting the neutral wire on the safety stat and fiddling with it on the start up sequence and after a few attempts the boiler again fires up. This whole cycle is continually repeated.
I can make the boiler stay on if i run a hot tap when it fires initially, but obviously this keeps the water sometimes hot and sometimes just luke warm, if the radiators were already hot then this seems to be maintained.
From my analysis i have come to the conclusion that the gas valve is the problem, but more specifically i think it is the solenoid.
Very basically all that seems to be happening is when the boiler switches off (due to modulation) it cannot fire up again because it cannot get the valve to open without me messing with the safety stat.
How do i confirm my anlaysis of the solenoid problem? How can i test the resistance of the coils? Do I have to remove the solenoid or the whole gas valve? Is it possible to remove just the solenoid if thats the only way to test it?
Anyone else had a similar problem with this boiler? The engineer also said that SIME used to be part of Halstead, is this true and if so does anyone with a Halstead recognise this problem?
Any help is much appreciated!
Thanks
I've spent 2 weeks trying to isolate the problem with my boiler. It gradually ground to a halt, it began by only firing after a reset then it only came on in the evenings for a few hours.
The fault light I am getting is telling me it was the air pressure switch which i have tested, also tested the fan and the pump and I've changed the ignition transformer and the safety stat (after being told these were defintely the problem by a CORGI engineer)
I've tested the PCB and confirmed that it is sending the correct voltage to the safety stat and the gas valve.
Whilst changing the safety stat I accidently left the power on and something happened which fired the boiler. I decided to play about with the safety stat connection, when i fiddle with it on the start up sequence i can get it to fire the boiler, when the temperature in the rads reaches optimum level the burner shuts down (I am presuming this is because of the electrical modulation of the gas valve)
After a few seconds the boiler trys to fire again and it cannot do it so i get the fault light again. I can make it fire again by repeating the above procedure of disconnecting the neutral wire on the safety stat and fiddling with it on the start up sequence and after a few attempts the boiler again fires up. This whole cycle is continually repeated.
I can make the boiler stay on if i run a hot tap when it fires initially, but obviously this keeps the water sometimes hot and sometimes just luke warm, if the radiators were already hot then this seems to be maintained.
From my analysis i have come to the conclusion that the gas valve is the problem, but more specifically i think it is the solenoid.
Very basically all that seems to be happening is when the boiler switches off (due to modulation) it cannot fire up again because it cannot get the valve to open without me messing with the safety stat.
How do i confirm my anlaysis of the solenoid problem? How can i test the resistance of the coils? Do I have to remove the solenoid or the whole gas valve? Is it possible to remove just the solenoid if thats the only way to test it?
Anyone else had a similar problem with this boiler? The engineer also said that SIME used to be part of Halstead, is this true and if so does anyone with a Halstead recognise this problem?
Any help is much appreciated!
Thanks
