Boiler help pleease

[crazychic]

Heya - love this website and forum. I am looking for some guidance please to help me with my studies. I have been searching the net and cannot find one exact answer to my point.

Anyway I am trying / hoping to learn how a boiler operates.

I know there are many variations and some older types have permanent pilots and thermoelectric vales/thermocouples which use piezoelectric spark ignition.

But nowdays most new boilers have mains spark ignition and use a flame conduction and rectification fail safe device instead of the more traditional thermoelectric valve/thermocouple.

Is this how a fan assisted boiler fires up... please correct me if any of it is wrong, missed out or can just offer me any extra help please.

1) Signal from external control, ie room/cylinder thermostat calls for heat
2) Fan starts
3) air pressure switch or thermistor detects negative pressure and signal PCB that is is OK
4) Pilot solenoid is energised allowing some gas through to pilot burner
5) Mains ignition sparks electrode, which lights the pilot
6) Flame conduction electrode senses flame and this (via the relay) operates the main solenoid valve which allows gas to the main burner
7) gas is ignited in main burner by the pilot, which is already lit

I know some boilers use different variations, some do not even have a pilot and just allow a small gas to the main burner to be lit first, etc.

Also some boilers do not use a boiler stat and use thermistors on the flow and return instead.

With the fan, some boilers have thermistors here instead to detect a negative pressure instead of the air pressure switch and hose (s).

Some also have a Flow Switch - but I am not exactly sure what this does/is instead of yet?

 

[Agile]

Why dont you go on a college course and also buy a good book on boilers?

Tony

 

[crazychic]

Agile - I do actually go on a course. But I am nearly finished Level 2 and have been looking up Level 3 in advance. I am trying to understand a lot now as Level 3 is a lot harder and I want to get a head start!!

I also have books, by R.D. Treloar, Heinemann, Steve Muscroft, Blower, and a Combination Boiler book by John Reginald.

All have slight variations though and I was just trying to check my progress with experienced people who may be able to help/correct me.

All above I have taught myself over the past 4 weeks. It is hard to understand at first, especially on your own, but I enjoy learning about it!

 

[spacethegas]

take a look at various boiler installation & service instructions.

they generally list a sequence of events.

also checking through the fault finding procedures will help.

theres plenty here to get you going.

http://www.partsarena.com/baxi/

flow switches are generally on the water side & detect flowing water or pump operation.

air flow sensors have been used instead of an aps.

theres an air flow sensor on a potterton lynx to start you off.

good luck.

 

[gas4you]

I would generally expect the pump to start and be proved before the fan.

 

[spacethegas]

I would generally expect the pump to start and be proved before the fan.

on a combi or system boiler.

 

[crazychic]

Thanks for your help and I will get my hands on a few boiler manuals now!

One thing that is still not 100% clear, and I am trying to work out on my own! Is.. when a boiler with non permanent pilot is satisfied (ie from the room stat being satisfied), does the gas supply just instantly shut off, via the solenoid's de-activating, to both the pilot and main burner?