Pilot light keeps going out

[droxford]

Boiler : Glowworm Swiftflow 75 combi.

Problem : With central heating swiched off the boiler works fine and DHW on demand. With central heating switched on pressure rises from 0.7 bar min to 2.5 bar over a period of 25 mins. At this point the pilot light goes out and will not stay lit (manual lighting with SIT valve) until the boiler has been left for about 10 mins.
I have noted that when the heating is on and the flame is full the that tip of the thermocouple glows red; is this normal?



I have had fitted a new auto bleed switch, fan and boiler overheat switch.

Many thanks in advance for comments

 

[corgigazza]

Is the pump working it does not work on hw but gives circulation to rads for ch also do a search for re charging ex vessel

 

[droxford]

Thanks.

All the rads are hot and the pump changes note if turning the speed down, so I would assume to be working. I have noticed however that if a hot tap or the shower has been running then when switching it off, a sound like rushing water can be heard through the downstairs rads (CH off).

What would be the max pressure expected with the CH working. Min pressure should be 0.7 bar.

What is a ballpark labour figure to have a new wall mounted combi fitted? I maycut my losses and go for new.

Cheers

 

[corgigazza]

sounds like airlock, is aav working,are rads all bled.

 

[droxford]

aav was replaced and all rads bled by plumber. After that he sort of gave up, suggested that I replace the pressure relief valve (leaking) and the boiler overheat, (both done) then replace boiler and left.

As the boiler is approx 10 years old then if replacement is the only option then so be it. But I would hate to have replaced it when there is something simple causing the flame cut-out

 

[chrishutt]

With central heating switched on pressure rises from 0.7 bar min to 2.5 bar over a period of 25 mins.

This is symptomatic of a failed expansion vessel. Why have you not checked this? Do you really want to spent several thou' on a new boiler rather than check the expansion vessel?

 

[corgigazza]

When the plummer fitted aav did he also fit the adaptor to enable the aav to be removed with the system pressurised (1/2 hex nut ) if so these stop the aav from removing the air as they jam the workings. drain down and remove the adaptor refit aav. also check the fan runs constant

Also remove and check pump head as have had the impellor head shear off before, leaving shaft turning on its own. esp on wilo pumps

 

[droxford]

As far as the expansion vessel is concerned, I have pushed in the valve and no water could be seen. I have de-pressurised the system and attached, with difficulty a pump and pressurised to 1 bar, is this enough?.
Then refilled system to 0.7 bar and tried. The gauge still went to 2.5 bar in 25 mins and then the pilot cut-out.

I must admit to having great difficulty with the ex vessel because whenever I removed the pump connector pressure was lost and when reconnect there was no pressure whatsover so I can never be 100% sure of the pressure on the air side of the diaphram when finished.

Regards and thanks

 

[chrishutt]

I must admit to having great difficulty with the ex vessel

So how do you read the pressure of the expansion vessel? What gauge do you use?

 

[corgigazza]

The pipework/flex hose that connects the vessel to the boiler may also be blocked, with the system on .7 bar repressirise the vessel if the pressure gauge does not rise as you pump the vessel to 2 bar the hose is also blocked, sounds like you need corgi engineer brit gas now take on boilers not working

 

[droxford]

So how do you read the pressure of the expansion vessel? What gauge do you use?[/quote]

The gauge was attached to a footpump

Thanks

 

[corgigazza]

foot pump gauge reads ex ves press
boiler gauge reads system press

 

[chrishutt]

Well I know that - I was just trying to see if droxford was using the right gauge for ex. vessel pressure.

To do the ex. vessel pressure properly, the boiler system pipework should be open to air (e.g. via air vent or drain point) - pump up to 1.0 bar on foot pump gauge, then wait a little (30 seconds?) to see if pressure is held or not - for this you need a good airtight connection between schrader valve and pump connector. If not, the diaphragm in the expansion vessel may have a leak.

 

[corgigazza]

Looks like you have 2 faults
1. the pressure rising, does not allways the overheat to trip

2. the o/h tripping may be caused by
all trv closed down (pins jammed shut), no bypass is fitted on these boilers so a manual one is normally fitted (brass gate valve).
Airlock
Blocked pilot injector
faulty pump
faulty thermistor
Faulty fan

 

[droxford]

Thanks for the info.

The ex vessel is holding pressure so I switched on the CH. True to form after 25 mins the pressure gauge was showing 2.5 bar ( all rads hot) whereas the pilot went out.

It seems worse now because after 15 mins with the pressure gauge now showing 1 bar I cannot get the pilot to relight, so not even hot water now.

The fan was replaced early in the year because the bearings had seized, all the rad valves appear to operate, ie the pins are not stuck. The ex vessel appears to hold pressure. The auto air vent and PRV have been replaced by a plumber. The boiler overheat switch has been replaced so has the thermocouple. I guess this leaves the motor which has been mentioned previously and it is a Wilo but I cannot see how to make sure the impellor has become detached.

More importantly now however is what is suddenly stopping me from relighting the pilot.

Regards