Protherm 40 - 50 CI ignition sequence please?

[Davebullock]

Hi,
Can anyone tell me the operational sequence in STEP by STEP detail of how this boiler lights please?
This boiler has 4 neon status lights and N3 and N4 are NOT lit. The fan cycles and the boiler doesn't light.

What I know so far:-
I checked what happens as the fan starts up. I generates a differential pressure across the pressure switch which operates a micro switch. This switch seems to control power to the fan so as it opens the fan goes off, (hence it cycles).
I figure that something should supply power to the N/O side of the micro switch to keep the fan running?
There appears to be NO igniter operation.
So if I knew the sequence of how all these items are supposed to interact I might get a clue as to what is wrong.
Can anyone help please?
Thanks in anticipation.
Dave

 

[Jackrae]

Switch is not there to keep fan running, sounds like a control board failure. Here is the installation & service manual, with fault finding from page 25 onwards
https://www.heatingspares247.com/do...r_Installation_and_Servicing_Instructions.pdf
You are presumably aware of the legal implications of working on your boiler

 

[Davebullock]

HI thanks for your speedy reply, I already have this manual and started to go through the checks.
However whilst it provides an "if this do that" guide (which ends up at "replace pcb") it doesn't help understand how it is supposed to work!
If I knew the startup sequence I could find what was missing to cause it to fail.
For instance the fan may come on and start the igniter which should light the pilot, Then the main flame should fire up, this may then cause power to be applied the N/C contact of the pressure switch which in turn would then keep the fan running. (won't know until I am forced to trace the pcb out)

Yes I understand the legal implications, having been in the trade... albeit working on industrial gas turbines.
Thanks
Dave

 

[Agile]

Be aware that forum rules prevent us giving detailed advice on gas/combustion problems here.

So apart from giving you the manufacturer's instructions that's probably all you are likely to get.

But I would have expected that you would be able to work out what the sequence is going to be. If not then my advice would be to not try to repair the boiler.

In any case do you really have a flue gas analyser to check the combustion and set it up correctly?

Tony

 

[Jackrae]

"Typical" sequence may well be something like this - but it all depends on boiler control circuit design :

a) system calls for heat
b) flue fan starts up and when creating sufficient differential pressure the pressure switch you refer to operates
c) purge sequence runs for a predetermined time
d) following purge sequence ignition sequence commences
e) some time later gas valve is opened
f) if suitable flame is detected then ignition sequence is terminated
g) provided differential switch remains operated AND flame remains detected boiler operation continues

The fact that the switch may have change-over contacts does not necessarily mean it holds in the fan. It may simply be a means of detecting/ensuring that some silly b*gger hasn't simply bridged out the switch ie if the contacts do not transfer over at the correct point in the sequence the control board may inhibit sequence continuation.

From personal experience, working on a gas-fired RB211 derivative isn't quite as much fun as a domestic CH boiler.

 

[Agile]

I would have expected that a RB211 style GT would be far more stable than a domestic boiler as well as carrying far more instrumentation.

Tony

 

[Agile]

I would have expected that a RB211 style GT would be far more stable than a domestic boiler as well as carrying far more instrumentation.

Tony

 

[Davebullock]

HI,
Thanks, it looks like there isn't 240V getting to the pilot multifuntion control solenoid. There's 35ish volts ac so I now don't know whether this is simply supplied via a relay contact (dry joint suspected on pcb) or a semiconductor switch. (more serious)
I am wondering if the same goes for the ignition circuit or whether the system never gets that far through it's sequence to try to ignite.

Spare pcb's are cheap on Ebay so may just get a replacement.
Thanks for your help.
Dave

 

[Jackrae]

I was joking
The nicest ones I worked on were the dual fuel (diesel or gas) Solar Centaur units installed in an eastern desert area. These used a diesel fired Solar Titan gas turbine as a starter motor, small enough to fit into a car !! Once the Centaurs were running on diesel the switch to gas was beautiful and simple - one fuel valve mechanism for both fuels operated under speed control. Some designs of turbines tried to ramp one fuel on whilst they ramped the other off. Almost impossible to get decent change-overs. The Centaurs turned second fuel on whilst first was still feeding then altered speed valve to compensate then turned first fuel off and again set speed valve. The whole operation completed in a blink of the eye.

 

[DP]

In any case do you really have a flue gas analyser to check the combustion and set it up correctly?

Tony where in the manual does it say FGA necessary to check the boiler. This boiler possibly predates the time when use of FGA was a dream, hence no test point fitted on the flue system, therefore use of flue gas analyser not required