Still struggling with WorcesterBosch240RSF

[DonDiy]

Worcester Bosch 240RSF combi boiler.
Soft water, high mains pressure.

Pilot light is on, but burner doesn't fire up when demand is created.
I've tested the pump electrically and it's working.
I've also noticed that the green 'demand' light on the front panel does not light up regardless heating or hot water demand.

I had replaced the pump head a couple of weeks ago as the old one's bearings were worn.
Heating & hot water from the kitchen taps was operating nicely. The cold pressure was about 1 bar and when operating was around 2 bar with no fluctuations.
All OK for a couple of days.
Then when running a bath, the water was initially hot and then cut out. Tried with all the rads off, but no change. Now the heating wouldn't operate either.
Remembered a previous fault when I replaced the diverter valve, so I cleaned out the valve, and replaced the diaphragm which was rotten and worn through.
Filled the system, bled rads, etc, all water tight. Diverter Valve operates when hot tap turned on, but - still no heat or hot water.

The problem now I would guess is electrical, but how do I decide where the fault is? Operating switch appears OK, can't see any loose connections.
Can anyone advise, please?

 

[twgas]

does the pilot stay on when there is no demand?

 

[clf-gas]

Pilot light is on, but burner doesn't fire up when demand is created.
I've tested the pump electrically and it's working.
I've also noticed that the green 'demand' light on the front panel does not light up regardless heating or hot water demand

GV knackered, not going to second stage (main burner).

 

[DonDiy]

Yes, pilot light is on throughout.

Another thing is the 'power' light is flickering and although the pilot light stays on I think I can see sparking.

GV - is that the gas valve?

 

[kevplumb]

yes

 

[clf-gas]

Yes, pilot light is on throughout.

Another thing is the 'power' light is flickering and although the pilot light stays on I think I can see sparking.

Check this and be sure as this could be your problem.

Electrodes spark and ignite the pilot, once lit the sparking should stop, has it?.
If no, the electrodes continue sparking when pilot is lit then this is flame rectification fault, this will stop GV (gas valve) going to main burner.

 

[DonDiy]

I was sure it was continually sparking last night, but I've just checked again and now I can't see any sparking.
Beginning to think I'm hallucinating.

 

[jockskinner]

Hi there,
I have a simolar problem on my 240. My hot water is ok but when I swich to heating its pot luck what happen. Normally there is one click and then the burner ignites. Lately sometimes there is nothing but a fan or pump running....not sparking and no ch burner ignition. Other times there is multiple sparking or clicking sounds followed by the occasional burner ignition which goes out after a couple of seconds and repeats the sequence numerous times before it usually goes ok. Today nothing all morning and then instant first time switch in the evening.Weird...
Cant seem to get to the bottom of this strange intermittent fault.
Jock.

 

[bengasman]

Hi there,
I have a simolar problem on my 240....

Tut, tut, Jock, no hijacking allowed on this here forum

 

[jockskinner]

Hi Bengasman,

Desperation is a terrible thing.

Sorry.

Jock.

 

[tomy]

I had to change the main pcb on one of these last week , sometimes it would work and sometimes it wouldnt , when I removed the old pcb you could see the contacts on the relay were black making the boiler work sometimes but not others .

 

[sourcebranch]

Are we maybe going in a bit deep?
Have you tried reseting the overheat stat?