Glowworm Fuelsaver MkII Main Burner Not Lighting

[Johnglav]

Hi,

I've got a gas Glowworm Fuelsaver MkII (Model 50R) and the main burner is no longer igniting.

The central heating has been poorly for a while with odd radiators being cold and the boiler being noisy when first switched on in the morning. When the system was drained, cleaned with Fernox and refilled the problem moved between radiators, but remained.

A friend helped me to power flush the system, but during the procedure when we needed to heat the system, the main burner lit and then went out after 15 seconds. We turned up the thermostat and the main burner reignited, but again went out after 15 seconds. After this the main burner refuses to light. The pilot light stays on and re-lights fine if we turn everything off and back on again.

We completed the power flush which got rid of a lot of sludge, but the boiler still refuses to relight. I tried a new switch and thermostat, but it made no difference. When I tap the gas slide switch, the pilot light goes out (this may or may not be relevant).

Any advice would be gratefully received.

 

[chrishutt]

You need to work through the fault finding section of the manufacturer's instructions. Not difficult if you can think logically. These will identify the likely fault. I would guess it might be something to do with there being air in heat exchanger and consequent cut out by over-heat stat, but others will know this boiler better.

 

[Johnglav]

Thanks for that, unfortunately the previous owner left me no documentation!

 

[chrishutt]

I'm sure Glowworm would be happy to supply new copy. You might even try their web site - they just might have downloads available.

 

[ollski]

check that the system is fully bled of air and that the pump is working.

 

[Johnglav]

Thanks for the suggestions, I've looked on the website for documentation, but it's an old model and I couldn't find any references. I'll check again. The system was fully bled (as far as radiators go), is there anything else to bleed?

 

[Johnglav]

Oh, and the pump is working!

 

[chrishutt]

The flow and return pipes leave the boiler at the top. Do they continue to rise, or do they turn downwards? If the latter, air will not clear fro here unless there is an air vent.

Also check if you have 24 volts a.c. to gas valve. If not, check the boiler thermostat and the programmer settings. I'm assuming that the pilot light remains alight.

 

[ollski]

Thanks for the suggestions, I've looked on the website for documentation, but it's an old model and I couldn't find any references. I'll check again. The system was fully bled (as far as radiators go), is there anything else to bleed?

Yes bleed the pipework, there will be a vent cap or two on a vertical rise of pipework somewhere....maybe the airing cupboard or the loft. Did you fill it with the motorized valve(s) hinged open on manual?. It will be the boiler getting to temp very quickly because no water is circulating, either because of air or a duff pump.

 

[Johnglav]

Thanks for all the responses. Just to answer the questions (as best I can) and clarify the position.

1. The flow and return pipes leave the boiler at the top. They continue to rise. There is a vent (vertical pipe with screw top alongside the hot water tank) in the roof space, which has been bled.
2. I'll try and check the gas valve 24 volts a.c. The boiler thermostat has been replaced without any improvement. Yes, the pilot light remains alight, unless you tap it with a screwdriver, then it goes out! (but relights ok).
3. Didn't touch the motorized valve(s) when filling. Is this a problem?

Just to clarify since the main burner went out at the start of this episode, it's never re-lit again. The 15 second burns no longer happen.

 

[ollski]

If there is 240v at the gas valve and it isn't opening its knackered, but I would check all the connections first especially at the thermostat and check it switches to a closed circuit when turned on.

 

[chrishutt]

Gas valve operates on 24 volts a.c., not 240. There is a transformer, and a combined thermostat (24 v) and pump overrun (240 v). Overheat stat interrupts thermocouple circuit.

There should also be a by-pass (a 15mm pipe connecting flow and return, probably near the boiler, with a gate valve on it. This would normally be opened just enough to allow the minimum flow through heat exchanger at all times. Has this been altered in the course of your flushing, etc.?

You could open the by-pass fully to see if it makes a difference. If the main circuits are blocked, flow through the by-pass may be sufficient to clear something. Alternatively, if the by-pass is open too much, the pump may not be able to clear something (e.g. air) on main circuits, so you could also try closing it fully.

It should be possible to manually open motorised valves to clear air, etc. Look for lever - what make are they?

 

[Timmo]

If I am recalling the right boiler the problem may be around where the over heat stats connects into the gas valve.

if so the connection may be dodgy, which is a common fault. It is usually a very temperamental connection at the best of times. this is why when you tap the gas valve the pilot goes out. Make sure that all the connections are cleaned with wire wool and that it is not worn where the seating is.

Hope I am not on the wrong track (or the worng boiler for that matter)

regards

 

[ollski]

Gas valve operates on 24 volts a.c., not 240. There is a transformer, and a combined thermostat (24 v) and pump overrun (240 v). Overheat stat interrupts thermocouple circuit.

I don't know it chris so I take your word...my reference material just tells me it is the same as a 30c, which is 240v and my spares list just mentions a special gas valve with no insication of the solenoid voltage.

 

[chrishutt]

My info came from MI for Fuelsaver 50B Mk II, G.C.No. 41 315 95. Perhaps Johnglav can confirm that this is correct.