Explosions when gas ignites

Discussion in 'Plumbing and Central Heating' started by alwaysworried, 24 Mar 2012.

  1. alwaysworried

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    Hello: I am new to this forum, so please bear with me if I do something wrong. Can someone please advise me about my MAIN Medway Super Multipoint gas water heater? It is about six years old — no more than that.

    About ten months ago, a new regulator was fitted. I am not sure, but I think that it might be giving trouble again. This heater was serviced about four months ago because the pilot light was always very low. Cleaning it out cured that. However, just when the engineer gave a test run for hot water, it did what it had been doing for some time — after a couple of seconds of delay in igniting, when the gas did ignite, it gave a loud bang, and this blew out the pilot light. The engineer made some remark or other about it, but did not look into it, and left. The explosions continue (sometimes they are startlingly loud), but not every time the hot tap is turned on. Mostly, they occur when the hot water has not been run for a while (maybe after fifteen minutes, and, of course, after much longer periods of inactivity). If it has just been run couple of minutes ago, and then turned on again, the ignition is swift and quiet.

    I have tried advancing the "slow ignition" screw but this has not cured the problem.

    The heater had a new diaphragm fitted about six months ago. This fitter (one different from the one that has cleaned the heater) pointed out that the diaphragm pin was a bit bent. To save him time, I took it into my work shed, and straightened it with great care. The engineer was satisfied with it, but I mention this just in case it is relevant.
    Can anyone advise me what is wrong, and how it may be fixed? I am afraid of the expense of having a new regulator/gas valve put in, seeing that the one we had put in did not last for more than nine months or so. It is now out of guarantee. Though Heateam (a subsidiary of Baxi, who made the heater) will fit one for £169.00, the money has to be paid up front, and I have not been impressed by their attitude, so prefer not to use them. However, if a private engineer were to obtain and fit one, the price of the part would be about £320.00 (so I am told). Then there is the labour charge in addition.

    Also, if you don't mind me asking: on this heater, is the regulator the same as the gas valve, or are they different parts?

    With hopeful thanks, in anticipation of a helpful reply to all my questions,

    Alwaysworried. UK :(
     
  2. Space cat

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    The gas is taking too long to light. When it does eventually light there is more gas in the combustion chamber than there should be, hence the explosions. I had this problem with a water heater in a caravan many years ago. If I remember rightly, I fixed it by cleaning out the pilot jet to get a better flame but I see yours has already been done.

    The next place I would look would be the burner bars themselves and the main jet. (It's hard to be more specific without seeing the thing.) In our old heater, the main jet was at the back and the pilot was at the front. Blocked burner holes or a partially blocked jet would restrict the flow of gas to the pilot area. Come to think of it, low gas pressure would have the same effect.
     
  3. alwaysworried

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    Hello, Space Cat, and thanks very much for taking the trouble to reply, and so promptly, too.

    In view of what you say, am I not to think, then, that it MIGHT be the gas valve that is causing the trouble? The fitter that serviced this heater said that it CAN ONLY be the gas valve. Maybe, when he serviced the heater, he did not clean out the jets of the burners, and maybe he said what he did in order not to be accused of skimping the job. I notice that you make no reference to a possibility that the gas valve is faulty. (Since the regulator is less than twelve months old, I should not think that this is very likely.) I am assuming, temporarily, that the gas valve and the regulator are the same thing.

    I have had some bad experiences where heating engineers/fitters are concerned. That is why I am seeking truly impartial advice etc., on this forum.

    To press my earlier question, do you know, Space cat, whether the gas valve on this heater is the same as, or different from, the regulator? By regulator, I don't mean the knob on the outside of the case (nor the connecting tube that turns when you turn the knob). I mean the part inside the heater that these things modify.

    Thanks in advance for a reply.

    A.
     
  4. namsag

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    Its Not the gas section at fault , and no way would i trust a straightened pin that is asking for a large bang after the tap is turned off.
     
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  5. DP

    DP

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    Alwaysworried, how do you know you will get impartial advice here. This forum is visited by heating engineers, plumbers, would be plumbers/ heating engineers, DIYers good and bad not forgetting general dogsbody who can handle a screwdriver. Of these who do you think is going to give you PROPER impartial advice here? Did you check plumber's credentials for gas competancy or was your man a plumber with no knowledge of gas systems. If you checked his gas card, what did it say on the reverse?

    As Namsag says, forget the gas valve or what you refer to as the regulator (which it is not). Suggest you check if the lads who 'fixed' you boiler are indeed registered to work on gas appliances or are these people ones the Watchdog biker and rider go hunting for
     
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  6. Agile

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    To be fair these are a very old design which has been around for about 50 years!

    A friend has an open flued Ascot in his bathroom. when I point out the dangers he just says he can lay in bath and see the flames are blue and knows he is safe.

    The number of current engineers very familliar with them is rather few.

    Tony
     
  7. libby lou lou

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    Is this a back door to the CC.?
     
  8. namsag

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    Agile by your comment you are obviously not one of the few who knows how theses work.
     
  9. alwaysworried

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    Namsag: Thanks for the cautionary note. However, I always find Gas Safe/Corge reg. engineers. Just because they have these credentials, they are not necessarily straight, or caring tradesmen.

    I have had some bad experiences where heating engineers/fitters are concerned. That is why I am seeking truly impartial advice etc., on this forum.
    [/quote]

    Alwaysworried, how do you know you will get impartial advice here. This forum is visited by heating engineers, plumbers, would be plumbers/ heating engineers, DIYers good and bad not forgetting general dogsbody who can handle a screwdriver. Of these who do you think is going to give you PROPER impartial advice here? Did you check plumber's credentials for gas competancy or was your man a plumber with no knowledge of gas systems. If you checked his gas card, what did it say on the reverse?

    As Namsag says, forget the gas valve or what you refer to as the regulator (which it is not). Suggest you check if the lads who 'fixed' you boiler are indeed registered to work on gas appliances or are these people ones the Watchdog biker and rider go hunting for[/quote]
     
  10. alwaysworried

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    Thanks, DP, for your cautionary note. I mistakenly thanked Namsag for it.
    I have had some bad experiences where heating engineers/fitters are concerned. That is why I am seeking truly impartial advice etc., on this forum.
    [/quote]

    Alwaysworried, how do you know you will get impartial advice here. This forum is visited by heating engineers, plumbers, would be plumbers/ heating engineers, DIYers good and bad not forgetting general dogsbody who can handle a screwdriver. Of these who do you think is going to give you PROPER impartial advice here? Did you check plumber's credentials for gas competancy or was your man a plumber with no knowledge of gas systems. If you checked his gas card, what did it say on the reverse?

    As Namsag says, forget the gas valve or what you refer to as the regulator (which it is not). Suggest you check if the lads who 'fixed' you boiler are indeed registered to work on gas appliances or are these people ones the Watchdog biker and rider go hunting for[/quote]
     
  11. Space cat

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    Sorry but I don't - and without the thing in front of me I can't even begin to work it out. :( :( :(

    How right you are:

    QED!!! :rolleyes: :rolleyes: :rolleyes:

    But one bad apple doesn't mean the whole batch is off. Programmes like Rogue Traders and Cowboy Builders should copy the example of Crimewatch and finish with a message along the lines of:

    "Cowboys are really quite rare so don't have nightmares."

    You need a second opinion from a decent gas engineer. :) :) :)
     
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  12. Agile

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    In fact serious cowboys are so rare the TV programs are said to have to use actors as thats cheaper than waiting for a cowboy to to turn up.

    Tony
     
  13. compheat

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    When you turn the hot tap on the water section/diaphragm lifts and push's a rod into to gas valve which then opens and lets the gas through.
    If the push rod is slightly dent then its possible that this is the problem.

    !0 months ago a new GV was fitted, 4 months ago you had it serviced, and 6 months ago you had work done??

    I can only assume that none of the gas fitters new what they were doing otherwise it would be fixed by now :confused:
     
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  14. gaswizzard

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    This must be one of the simplest units to work on/diagnose (mechanical) , get someone who knows what they are doing (not difficult :LOL: )
     
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  15. alwaysworried

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    Thanks for your comments, Compheat. What you say about a bent pin may be true, of course. Also, your suggestion about the abilities of the three fitters I have had, are no doubt correct. However, even when the diaphragm pin was quite bent (i.e, at first), the explosions did not occur. In fact, even after the new diaphragm was fitted (this is when I straightened the pin), they did not occur right away. They started later on, some time after the new regulator/gas valve had been fitted.

    I have been wondering whether the diaphragm started to lay a deposit on the pin, which might conceivably have been scratched, unknown to me or the fitter. It might then have started to stick on the deposit of rubber on the pin.

    However, if the diaphragm is sticking on the pin, for whatever cause, how is it that when the hot water tap is turned on very soon after it has been running previously, the ignition is always quick and smooth, with not a trace of an explosion?

    The reason for my trying to fathom what is causing the explosions is that, if I ask a fitter to come round to have a look, he might think the cause is something else (like the gas valve, as one fitter has already suggested —with £400.00 to pay for a new one to be fitted), and, while leading to great expense, it might not cure the problem. Also, a fitter is not likely to be willing to wait long enough (say 15 minutes) while doing nothing. He might turn the tap on quite soon after an explosion, hear no explosion this time (which he would not, as I have described above), and declare that he has cured the problem — then goodbye, and thanks for the cheque!

    If it were certain that I could call a fitter and have the thing cured for certain, I would do so. However, in the last 18 months, I have spent so much money on this heater, that I have become very cautious. That's why I am sounding out the brains on this forum!
     

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