Buzzing Gas Valve on Glow Worm Fuel Saver MK II Model B

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Hi All,

First post.

We have had new radiators fitted which did not appear to be getting as hot as expected. So a new thermostat was fitted to the boiler. Boiler worked correctly for ~ 13 hours and then started to buzz. Buzz was diagnosed as faulty gas valve. The gas valve has been replaced and for the first couple of hours boiler appeared to work perfectly. However shortly afterwards, we were back to the situation where after a period of time the coil on the gas valve buzzes.

The boiler is a Glow Worm Fuelsaver MK II model B (GC Number 41 315 95). The original gas valve has been replaced with a SIT NOVA 820 24V (SIT 0820026).

It seems as if the bolier goes up to the temperature set on the thermostat, the thermostat then turns off the coil. When the thermostat then trys to turn the coil back on the coil starts to buzz and the boiler does not start. If the thermostat is turned off and left for a period of time the thermostat can be turned back on and the boiler starts without the buzzing noise.

Our heating engineer has fitted the old thermostat back into the boiler but the coil still buzzes after a short period of time. Initially when the old thermostat was fitted, the buzzing would start then immediately stop and the boiler would recover and continue to operate. However this only
lasted about an hour and the buzzing now results in the boiler cutting out completely. The engineer and myself have made a number of measurements on the bolier by following the fault finding guide and have observed the following:

When coil buzzes voltage across the coil is 13V - 17 V
When coil is not buzzing voltage across the coil is ~22 V
At all times without coil attached and thermostat on voltage across is ~37 V
At all times with thermostat off voltage across is 0 V

The above can be reproduced with the original thermostat or the new thermostat connected to the boiler. It seems that the coil starts to buzz sooner with the old thermostat fitted.

The fault finding guide in the servicing instructions state that with the measurements we have the coil has failed! Is it feasible that we have two coils that seem to fail when they "get hot"? I was wondering if any one on this board has had an experience of this type of problem?

Thanks,

Graham.
 
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Have you verified that the powersupply to the boiler is correct and the cables involved here have uncompromised insulation?
 
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But don't be too hard on RGI (?), as the buzz is normaaly a faulty valve.
 
Have you verified that the powersupply to the boiler is correct and the cables involved here have uncompromised insulation?

Have only checked the voltages going to the coil connected to the gas valve. Have not checked the the mains connected to the transformer or voltage from the transformer to the thermostat. I thought that if the two cables to the coil where receiving ~37V everything else would be OK. Could damage cables cause the type of fault I'm seeing?

Graham.
 
Transformer

Check output.Should be 24v

http://www.gas-spares.co.uk/Catalog...idaway/105120-BF/TRANSFORMER-GWSK8968[/QUOTE]

Do you mean check the voltage at the Transformers output pins or when it is in circuit with the thermostat? When it is in circuit with the thermostat it is at 37V and drops to 22V connected to the gas valve. I have not measured the output of the Transformer when it is not connected to the thermostat or gas valve.

Graham.
 
Do you mean check the voltage at the Transformers output pins or when it is in circuit with the thermostat? When it is in circuit with the thermostat it is at 37V and drops to 22V connected to the gas valve. I have not measured the output of the Transformer when it is not connected to the thermostat or gas valve.

Ok, when the buzzing occurs, I am assuming that the output has dropped (I can't explain why that should happen intermitently (yet)). This rduced voltage available may explain why the valve is chattering. When buzzimg test output. If reduced, test input. If input is correct then you are going to have to change the t'former. If output doesn't change between buzzing and non buzzing, then fault lies between t/f and GV. It's always a mission to sort these odd faults, ans more so when you're not in front of the boiler. But with electrics, logic rules.
 
Ok, when the buzzing occurs, I am assuming that the output has dropped (I can't explain why that should happen intermitently (yet)). This rduced voltage available may explain why the valve is chattering. When buzzimg test output. If reduced, test input. If input is correct then you are going to have to change the t'former. If output doesn't change between buzzing and non buzzing, then fault lies between t/f and GV. It's always a mission to sort these odd faults, ans more so when you're not in front of the boiler. But with electrics, logic rules.

I will try and get these done tomorrow. I need to take a look at the circuit diagrams.

Graham.
 
These had a standard grey push button gas valve if i am not mistaken (robertshaw ones on the really early ones) why was a sit nova valve fitted
 
Honeywell 8600C was the original on these why as the Sit been fitted was it a Glow-worm genuine repalcement kit? :eek:
 
If output doesn't change between buzzing and non buzzing, then fault lies between t/f and GV. It's always a mission to sort these odd faults, ans more so when you're not in front of the boiler. But with electrics, logic rules.

The output of the transformer does not change between buzzing and non buzzing. So I guess it must be something to do with the thermostat, gv or wiring between them.

Graham.
 

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