My 10-year old boiler (conventional, open flue) has started smelling of gas when it fires up (and recently set my CO detector off). The flue and ventillation are all fine. I've checked the input and burner pressures and gas rate - all spot on.
The flames don't look too good - very yellow and look too big. All the burners etc. have been properly serviced recently and this hasn't fixed the problem.
regards, Alan
Make and model please?
On what basis do you state that the flue and the ventilation are all fine?
who carried out the service and what did it cover?
Yellow flames indicate insufficient air flow either because the air inlet to the burner is restricted in some way or the flue is not allowing all the combustion gasses out. As your CO detector is triggering I would suspect the latter. Yellow flames means soot which could well helpblock the flue even more. Do get this checked out before there are serious consequences. In the short term you couldback off the gas flow until the flames turn blue again. You will get less heat output but at least it should be safe.
Whoever checked the boiler over did not do a good job. Either get him back or use another reputable one to inspect and report the first one to CORGI
In message , Alan writes
= incomplete combustion = Carbon monoxide
Poor air supply? Blocked flue ? crud on the burners?
get it serviced properly
Potterton Kingfisher MkII
The flue has been smoke tested and draws well without leakage. Looking up the flue, there are no blockages - you can clearly see the inside of the terminal. The fins of the heat exchanger have been thoroughly cleaned and again you can see clear through it.
The boiler is in a utility room on the ground floor with a suitable vent. However, opening doors, windows etc. in the room or elsewhere in the house has no effect. The vents on the boiler are clear and all the spacing around the boiler is well in excess of the manufacturers specification.
A Corgi registered firm. Supposedly a full service. There are no deposits on the burners. They also claim to have cleaned the insides of the burners in accordance with the makers instructions. I've no reason to disbelieve them.
I have no intention of tackling any of this work myself. What I want to avoid is:
- paying another technician to do a full service, only for him to be "surprised" when the problem still isn't cured.
- paying somebody to install a new air brick, then installing a new flue, only for him to be "surprised" when the problem isn't cured.
- installing a new boiler simply because the problem can't be correctly diagnosed.
On a related note, how should I expect a competent technician to set about diagnosing this problem?
thank you for your responses, Alan
One obvious test would have been for the firm servicing the boiler to have used a flue gas analyser to measure the CO , CO/CO2, and O2 levels.
This kind of analyser has a probe which goes into a special port in the combustion chamber on some boilers or into the flue. It would confirm the situation and give figures as to how bad it is.
Yellow flames are still a strong indicator that all is not well.
I don't believe that it is a mandatory requirement for a CORGI engineer to have one of these, but considering that they start at about £200, there is no reason that somebody servicing boilers should not have one.
I would call back the firm that serviced the boiler, ask them to do these measurements and provide the figures. Then contact the manufacturer and ask them whether the results are satisfactory.
If they don't agree to this, then report them to CORGI and ask the manufacturer for the name of an authorised engineer of theirs.
.andy
To email, substitute .nospam with .gl
Blocked lint arrester? (Should have been cleaned as part of the service of course.)
It can't be mandatory -- I couldn't find a CORGI gas fitter who had one when running through them in the Yellow Pages. I mentioned this to Keston (having just fitted my Keston at the time), and the chap I was speaking to agreed that they mostly didn't.
Somewhat concerning in a way.
Quite a lot of the boilers coming onto the market, especially those with premix burners, seem to have use of a combustion analyser in the setup procedure - typically that the emission composition should be checked at low and high end and the gas rate adjusted to match the air supply from the fan at the given burn rate.
BG seem to have them, although this seems to be mainly so that they can just check the flue with the probe and pronounce the boiler OK without taking it apart. . One day's visits and they've paid for the analyser comfortably.
.andy
To email, substitute .nospam with .gl
Oh and do not use it until this problem has been addressed
I would agree with you but with reservations. There was very little point in owning an analyser for the majority of domestic boiler work. The situation is changing now since premix and modulating burners are becoming common. The emphasis previously has been to ensure that any products of combustion were correctly evacuated with no spillage or leakage from flue into room space, and that combustion was basically correct as viewed by flame picture and gas rate relying on the manufacturer making appliances to an agreed standard in the\first place. For commercial appliance service the situation is somewhat different and personally I'd never go near a blown gas burner without a full spec analyser its not possible to be certain that one of these is burning correctly any other way - too little air = CO due to incomplete combustion, too much air =CO due to flame chilling
The BG analyser is often only a minimalistic job giving CO/CO2 ratio readings and while satisfactory is not a full analyser
Yup!
Technology was fairly simple and a manometer on the outlet of the gas valve was good enough - right?
Largely similar to one another, and one could also time the meter, although I have never seen an installer do that.
Of the two boilers that I shortlisted, the Keston Celsius could be set up by checking the gas rate - the gas valve being preset. The manufacturer does give combustion gas figures for later checks.
On the MAN Micromat, that I eventually installed, an analyser is required for set up. Gas rate is checked and then top and bottom combustion gas composition is measured - there being gas valve adjustments for each. In practice, little change was needed, but at the extremities of the settings, CO does rise. There is no question of doing pressure tests at the gas valve. The nipple is there, but the pressure is negative.
Possibly beyond the comprehension of the average operative. They just seem to write down the number and that's it.
.andy
To email, substitute .nospam with .gl
Well the the correct approach is that you EITHER fix it properly: (blue flames [1], gas pressure at correct setting, gas rate 90-105% of nominal, flue clear and passes a flow test. ) OR you turn it off.
If the first guy is half decent he will be round pronto 'with tail down' when you say you have yellow flames from a open flued appliance and the CO alarm has gone off. There are no more lines of safety left, just fortuitous ventilation, timing & luck.
TRANSCO will give you an opinion but will (nigh on certain) condemn the appliance. HTH
[1] If using a combustion analyser then I'd reckon on CO/CO2 < 0.003 say.
Since the pressure and gas rate are correct, the flue clear and opening a door make no change the problem MUST lie between the injector(s) and the burners. There are often gauzes in the mixing tube which can get blocked with very fine dust.
More surprising is the CO alarm going off this implies the products of cumbustion are not being correctly drawn into the flue which is odd since it is apparently clear.
Anyway fixing (or even replacing) the burner should be the first approach but the alarm makes me think there is another problem to be found.
Check the inlet side of the flue isn't blocked by leaves, birds nests, vermin etc, anyone can get the burner to burn clean with the cover off, but put it back on and you rely on the inlet. British gas never checked mine and it went that way, pulled the flue from the wall and the inlet was clogged with leaves....
Oh really? That's what I ended up doing with my Keston. It was supposed to be factory set, but it was miles out. At the top end, it was (IIRC) 10% too low -- they only allow
+-5%. At the bottom end (which the instructions didn't even suggest checking), it was about 4kW instead of 7.5kW, which explained why the gas ignition was travelling back up into the premix area and making a sound like a 32 foot organ pipe. There is only one mixture adjustment, but fortunately it seems to have a much more dramatic effect at the bottom end than the top end, so it was possible to bring them both in much nearer to the rated values, although the top hit the correct value whilst the bottom was still a bit under.That is one of the checks on the Keston. I says something like it should be at least -1.25" -- it's not at all clear which side of the -1.25" is the 'OK' side, and it was off (can't recall which way). Having adjusted the power input via meter timing, fortunately it ended up being exactly -1.25" so I didn't need to worry which way was 'OK'.
That's 'cos you read the instructions.... :-)
That was my experience as well. The bottom end was more critical than the top and there was a certain amount of iteration.
Hmm curious.... Presumably that is at full burn rate?
.andy
To email, substitute .nospam with .gl
Yes. As the burn rate reduces, pressure moves towards zero. The instructions don't give values other than at full burn rate though. (This is all from memory -- I don't have the instructions here to check.)
This is a conventional flue not a balanced or fan assisted flue/duct.
Well, the original technician who serviced the boiler, then condemed it reckoned it needed a new burner assembly - "but the boiler was obsolete so probably wasn't worth repairing". I tried to get some other opinions
- one plumber never returned my call, another said he could fit me in
3 days later, but he never turned up...In the meantime, I found the service manual on-line, made myself a manometer with a bit of plastic tube, dis-assembled the boiler to check the lint arrestor and injector (all fine), did some smoke tests with some smoldering kitchen roll and found the heat exchanger still quite sooted (I know I said it was clear, but I am no expert and the bloke who cleaned it a few days before was...)
Spent a while properly cleaning the heat exchanger, then tested for leaks and inlet & burner pressure with the manometer and rechecked gas usage - all seemed fine, the yellow flames have gone, the CO detector stays off and the bad smell gone. So I peeled the "Immediately Dangerous" sticker of my boiler.
So if you hear of a large explosion in the Manchester area...
regards, Alan
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