Boiler won't fire up

[coldJohn]

I have an old potterton floor standing Kingfisher CF50 CAT 1 N been working fine get it serviced etc. now won't fire up piolt light burns electriain checked contols and says power is geting to gas valve, gas valve has been replaced ( by gas Eng)but still will not fire up. I have been told it is broken but not what is or why.
The boiler is so simple I would like to know what is stopping it working any ideas?

 

[Armo74]

Could do with knowing what controls you have.

 

[coldJohn]

one theromostat and a control box by Honeywell about same age as boiler(old) for C Heating/water which operates two motorised valves and the pump all of which work. there is what looks like a flow sensor on one of the pipes that goes back to the contol box, but all looks pretty standard stuff

 

[Armo74]

I take it he checked the motorised valves were operating correctly?

 

[coldJohn]

Yes they appear to work as the always have opening and closing depending on if CH or water or both required Electrian also checked for power at the gas value which there was, does the power open the gas valve?

 

[twgas]

is the knob on the gas valve to to main gas or has it been left on pilot, not all have a turn on/off knob, some have just a push button.

 

[coldJohn]

Gas eng was trying to get to fire and he serviced it so assume( dangerous I know) that he did turn knob as well as holding down button to light pilot

 

[twgas]

Gas eng was trying to get to fire and he serviced it so assume( dangerous I know) that he did turn knob as well as holding down button to light pilot

You had a gas engineer service a non working, open flue boiler! How did he test anything? Could he not diagnose ( they are pretty simple boilers)?

 

[coldJohn]

Yes had Eng look he decided it was gas valve, which has been replaced (twice)but still won't fire up so now he does not know what to try!
WE have gas, we have power to gas valve( right way round) but when thermstat switches on pump and water flows boiler does no fire up. ?
Given that it is such a simple design I am not happy to just give up and replace the boiler without knowing what is broken more than likley something silly. we need advice from an Eng who has spent time working on these older boilers and may have had similar problem, or just a knowlegeable eng who can figure it out? I won't ( can't) touch the gas side of things and Eng will come back if needed just out of ideas

 

[onecog]

there is not a lot to go wrong.You light the pilot,switch on your programmer,turn up the boiler thermostat and the boiler fires up.
Have you checked the main 3 amp fuse ?
Is everything switched on and calling for heat ?

 

[twgas]

I agree its a simple design.
I cant imagine you've had 2 new, faulty gas valves.
So that leaves an electrical problem, you say that is fine, been checked by sparky, or gas supply.
Have you checked the knob as i suggested earlier? (Always check the basics)

 

[onecog]

One other thought.
The ignition button you press to light the pilot has a flame mark on it ? (i think)
Have you turned this to line up with the mark ?
If not the boiler won't fire up.