Why does my boiler keep cutting out?

Discussion in 'Plumbers' Talk' started by Dangermouse79, Aug 23, 2010.

  1. Dangermouse79

    Dangermouse79 New Member

    Hi! I've been reading some threads in here and you all seem like a very helpful bunch so I was hoping you would be able to help a damsel in distress!
    I had problems with my boiler constantly tripping so I asked advice from a plumber and was told I should replace the 3 port valve, which I did (with help from my clever Dad!). Although this did solve the other problem I was having previously with the radiators heating up when just the hot water was on, the boiler only worked intermittently and cut out the rest of the time.
    We thought that the next logical problem was the pump, which had also been making some strange noises, so we fitted a new pump and (after lots of swearing and dripping pipes), the problem was actually worse! Now the boiler only fires and stays lit for a few minutes before the flame goes out and the little "overheat" button pops out.
    Both the valve and pump seem to be doing their jobs, because the valve changes position depending on whether you turn on the heating or the hot water and the first radiator in the system starts to warm up before the boiler trips. What is the next logical problem with the system?
    As far as I know it's a "glowworm" boiler. I don't know the technical name for the type of system but there is a hot water header tank and a central heating header tank and also a little valve near the tank that you can bleed with a radiator key!
    Can anyone help me with advice?
  2. tomplum

    tomplum Active Member

    the button that is popping out is a safety devise guarding the boiler from overheat, the usual cause is the pump not running good enough to take the heat away from the boiler, if your sure its not the pump, then it could be another circulation problem like a partially blocked pipe or a valve not fully open, and then again it just might be the overheat stat itself that is faulty, or even the main stat is faulty and allowing the boiler to overheat, maybe you need a better plumber to have a look :)
  3. Captain Leaky

    Captain Leaky New Member


    You have an airlock so the boiler overheats - either that or you have messed things up!

    get a plumber in!
  4. mainman

    mainman New Member

    are you sure you never fitted the new pump the wrong way round this would cause boiler to cut out
  5. Dangermouse79

    Dangermouse79 New Member

    Hi guys and thanks for the replies. I have a few further questions...
    1. How would I prove if there was air in the system?...all radiators have been bled and are full and so has the pump and the valve near the hot water tank. Is there anything there I have missed?

    2. If it is one of the stats, how much should I expect to pay a plumber to fit a new one? The plumber who came round to have a look in the first place was a friend of a friend who is now on holiday, which is why I'm asking you lovely people for advice instead!

    3. We fitted the new pump with the flow arrow pointing in the same direction as the old one....if the old one was fitted wrongly in the first place would we ever have had any kind of heating or hot water at all? Nothing would surprise me, considering the problems we've found since we bought the house 3 years ago!!
    Thanks again!
  6. Crowsfoot

    Crowsfoot Screwfix Select

    1. How would I prove if there was air in the system?...all radiators have been bled


    You can't really it's just a popular symptom of the problem you're having.
    I would drain the system again and this time refill it with mains water pressure (with dads help) this will blow out any air-locks in the pipes.
    Try a utube search on toms tips from the van, the one on mains flushing could be adapted in order to do this operation.
    Just an afterthought could anyone have turned off a gate valve on the by-pass?
  7. Dangermouse79

    Dangermouse79 New Member

    Thanks tapwrench. That is actually how we ended up filling the system the first time we drained it after fitting the valve because it wouldn't fill from the header tank. That was also what made us think it could be a dodgy pump. After fitting the new pump, it filled from the tank perfectly. I'll have a go at draining and filling again.
    Checked the bypass gate valve, which looks pretty crudded up on the outside but it was fully open. It was rather easy to turn though...as in I could turn it all the way round with my fingers?! Has the washer dropped off and clogged the system or something?
    Also, any idea how long a pump should keep pumping after I've turned off the demand for heating/water? It seems to keep going for a while!
  8. G Brown

    G Brown New Member

    If it would not fill from the header tank you should have asked yourselves "why"

    Stop fiddling and get a plumber in.
  9. G Brown

    G Brown New Member

    the gate valve has probably sheared off inside - there is no washer, just a gate.
  10. ThreadJacker

    ThreadJacker Active Member

    If the gate valve is sheared it will just turn and turn, if it comes to a stop it will be okay.

    They are very delicate so be carefull, if its sheared replace with a full bore lever valve.

    When you filled the system back up did you bleed all the bleed points?

    Aside from the radiators there should be others (cylinder coil?), look in the airing cupboard, if you vent them and nothing comes out they are clogged.
  11. Captain Leaky

    Captain Leaky New Member

    You have answered your own questions - the system would not fill properly- ipso facto there is a blockage which means there is probably still air in the system or very bad circulation.
  12. Dangermouse79

    Dangermouse79 New Member

    Just wanted to say thanks for all the advice! I seem to have fixed the problem with a combination of replacing the gate valve on the bypass, keeping the boiler stat turned fairly low and mains filling the system! Thanks again guys, much appreciated!
  13. AnnieMcK

    AnnieMcK New Member

    Hi there, Was just reading through this thread and wanted to share this with you - I had a lot of trouble with my boiler when I first moved into my new house. As I was tight for money because of the move I decided to do some googling before calling out an engineer. Luckily I struck gold as I came across a series of videos on YouTube by a company called corgi homeplan, they are incredibly easy to follow and helped me a fix a problem that I may have had to pay £100 or so to have an engineer come out and fix. This is the video that I used but there are lots of others on there that might help you!

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