worcester 18ri greenstar goes off when case refitted

[DerekJB]

Hi Guys wondering if anyone can shed a light on a problem I am having with this boiler, I got called to a house where the boiler was making a noise like it was being stangled with a bad case of flatulance on the side,
at first thoughts the fan was nackered as the boier kept going out on low modulation and admiited this sound, not sure so called W/B and they also said sus fan, so changed fan, no joy, still the same, so called W/B and spoke to engineer whilst boiler running and making a hell of a noise, put on analyezer and got Hi co2 [10.6] and got 7,6 on low setting so adjusted gas/air ratio under their guidance and got good readings, and no noise, shut boiler up went home, boiler never fired back, their diagnosis gas valve shot, so changed gas valve today set up ratios got steady read out as per book all running fine put back in normal running mode ran boiler for half hour and everything steady put cover on boiler died, took coveer of boiler fine, check all settings again and all in spec, put cover on and boiler wont run in low mode proir to main burn, take cover of and run and it,s fine, then put cover back on and it changes to low burn then goes off, it does try to re-light and runs for about 10-20 seconds then slowly dies, any help would be appreciated

 

[Nostrum]

Air intake all clear? no bushes growing in the flue terminal? Also what's inlet pressure at the valve?

Sounds like a poor mixture, lack of air which would also add up with the case having to be off.

Was the old gas valve the type with the large air adjustment screw in the combustion chamber?

 

[AWheating]

prob a flue problem/lack of air.

 

[desrob]

flue could be split, can you see it all

 

[DerekJB]

Hi Sam thanks for the reply, flue is all clear, gas at intlet 22.3mb air/gas at high burn 9.8/9 gas at low burn is 9.2 when casing is of boiler running fine but sound like its sucking air through a straw, I have never worked on one of these before so I am not sure what it should sound like with cover off, however when cover on it sounds quiet enough. the old gas valve had the bulbus bit at the front, and the big mixture adjustment scew in the black pipe above the valve,

thanks for help

 

[DerekJB]

flue seems ok it is only a short run of about 2/12 feet,
cheers

 

[desrob]

flue seems ok it is only a short run of about 2/12 feet,
cheers

leave it to some one qualified .

 

[Nostrum]

Yes that the gruppe valve I think it's called, and they are a pain in the arse IMO but you've changed it so no worries. Have you analysed it with the case on?

Also have you checked the heat exchanger, burner and sump? There is a test point on the air intake which you attach a gauge to, should give you a - reading in MBar. Not sure off the top of my head what it should be on an 18Ri but gives you an idea of whether or not it requires a full strip down of the burner. It's an older model so maybe it needs doing.

 

[Roger Welton]

only differance case on / off is air supply, I'd be looking for a restiction in air duct or POC being drawn back somehow.

 

[SimonJohns]

Set high fire. Leave FGA in. Replace cover. And check readings.

I would suggest setting the correct valves with the cover on using the above method. I have has this issue before. Especially with long flues

 

[DerekJB]

leave it to some one qualified .

I am a qualified gas engineer I just lack a bit of experience which is why I came to you experts,
cheers!

 

[DirksPlumbing]

I would go with Rogers opinion if the flue way is clear. Check for CO2 incoming. Would be just another flu where the seal is dangling out or not even there for what ever reason. Or "predrilled".

Just one thing makes me think, the combination of noise and smell.
To be on the safe side you should still mechanically clean both flue ways. You would not be the first that gets fooled by a cob web letting enough light through but not enough air.

 

[arran197]

Does sound like a fluing issue. If the flue isn't that long, I'd take it apart and look at it thoroughly. Also check the flue parts inside the boiler. I've seen a few Baxi flues split the exhaust causing a mix of POCs. It gave the same problem as you describe. It might be a seal out of place or has perished. Providing your inlet pressure and fan pressure (as above) are right, then I would go with this.

 

[kne11y]

I had this problem on an ideal slimline and as last post says the flue was not long enough I had to extend it by 2" the boiler had been fitted this way for 6 yrs and only showed fault yrs later.

 

[neily01]

This is why i like it when i see boilers now fitted with air sample points, you can quickly and safely confirm flue/seal issues.

 

[Danv44444]

Do Wb have venturis? I Had the same problem on a Baxi and it was the venturi inside the flue? there about £3 to buy.

 

[SimonJohns]

Do Wb have venturis? I Had the same problem on a Baxi and it was the venturi inside the flue? there about £3 to buy.

Worcesters use tachos

 

[mfgs]

I had one with a plume kit a few months back, the plume kit had come off the end and was half covering the outlet and it would not fire with the case on, but was fine with the case off. I would definitely be looking at a flueing problem.

 

[Danv44444]

What are Tachos? Are you telling me worcester use a crisp type material in there flues?

 

[Roger Welton]

Nah its to stop them driving more than the allowed hours in a day

 

[DerekJB]

Hi Guys thanks for all the suggestions, unfortunatley none of them were correct, it turned out that the sight glass at the top of the heat exchanger had gone into the burner causing the the burner to run at very high temp which damaged the gas valve and fan, which is also why it would run with case off but not when on as it got the extra air through the hole left by the sight glass, evidence found was cracked solenoid casing and discoloration, and soot inside fan vanes, hope this helps someone in the future,
thanks to all who replied to original question.

 

[arran197]

Bloody hell, that's a weird. Who did that then? Sounds expensive! Why Worcester felt the need to put a sight glass there is beyond me anyway, you can't see bugger all, even with that so called 'mirror'!

 

[Petefinny]

Its a case seal problem, had one of these before, everything looked fine andcould not solve the problem and had to give up and ring the manufacturers and get them to send an engineer! Spome times you just have to give up.

 

[vern]

Bloody hell, that's a weird. Who did that then? Sounds expensive! Why Worcester felt the need to put a sight glass there is beyond me anyway, you can't see bugger all, even with that so called 'mirror'!

They have been blanked off with a steel plates for the last few years now for this reason