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Glow Worm Fuelsaver Mk2 Boiler cutting out

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  • Glow Worm Fuelsaver Mk2 Boiler cutting out

    Hopefully someone may have an answer to my problematic boiler.
    The problem is that the overheat cut out keeps tripping. My engineer has replaced the pump, gas valve, boiler thermostat and thermocouple over the past few months but the problem still persists. We have recently flushed through after adding a system cleaner but still no improvement. His opinion, due to having replaced the obvious causes, was that the heat was not getting away from the boiler quick enough due to the pipework or heat exchanger being partially blocked. I can fully understand this point of view except for one reason.....
    When the boiler is lit and the controls are switched on, the boiler will flash up and run for a certain period of time. Once the water is at the temperature selected on the boiler thermostat, the main burners cut out leaving just the pilot, just as it should. However, around 15 seconds later there is a click and the overheat cut out shuts off the pilot. However, if for example I set the boiler thermostat to low, start it up and let it run until it cuts out, the overheat still clicks in after around 15 seconds. But, if I do the same again i.e. run the boiler with thermostat on low, then, as soon as it cuts out, I increase the temp on the boiler thermostat before the overheat cut out clicks in, the boiler will flash up and keep burning until it reaches the new temperature and then cuts out. The overheat still cuts in around 15 seconds after this.
    Surely, if the problem was due to heat not getting away from the heat exchanger, and the cut out tripping on a low temperature setting, then I would not be able to increase the boiler thermostat and get the boiler to burn for much longer?
    Any help appreciated.

  • #2
    That is a rather old boiler and as opposed to wasting money keeping it going it would be much wiser to fit a new one, cut your bills and have a warranty and solve your problem.
    Aside from that it appears to me the pump overrun thermostat may be at fault (it is part of the boiler thermostat). Does the pump keep running after the boiler thermostat gets to temperature? It should to disperse latent heat. If not electrical tests need to be done to see if it's the thermostat or has it been wired up correctly? Any decent engineer should know these things/be able to eliminate them. Not all parts are available for that boiler any more so it would be wise to start saving for a new one anyway.


    • #3
      Many thanks for taking the time to reply.
      Yes, I'm aware that its rather old and not as efficient as new ones, however, I have had conflicting advice on the economics of buying new. Firstly the high capital cost of buying and installing the new boiler together with the over estimating of the savings achievable, mean that it takes many years to see a payback from the increased efficiency. I'm also told that today's new boilers do not last anywhere near as long. Don't really know what to believe as its gas engineers giving me the advice from both ends of the argument. Added to that two engineers who have serviced this boiler in recent years both say its in really good nick for its age (prior to this current problem). However, I do realize that a new boiler will be required at sometime but cant afford at present anyway.
      In answer to your question, yes the pump does keep going after the boiler thermostat gets to temperature, and the boiler thermostat has just been renewed but did not solve the problem. What I don't understand is why the cut out operates 10 - 15 seconds after the boiler reaches temp at the lowest setting but will also only cut out 10 - 15 seconds after the boiler thermostat reaches temp if set at the highest setting.


      • #4
        You would save 30% minimum from a new boiler. Good makes have long warranties these days. Someone is just winding you up with their opinion as opposed to facts.
        It is very hard to diagnose without being there. Sometimes pump stats stick and you get a pause for a few seconds, long enough to overheat it, but then the pump is running again when you look. It would be interesting to attach digital temperature gauges. The click may not be the overheat but the gas valve pilot solenoid shutting. The overheat wants testing with a multimeter in fault conditions to prove. The thermocouple may be failing due to a poor quality pilot flame. The trouble is you cannot test any of these things and it will cost you to get an engineer to do it, more money wasted.


        • #5
          The longer you wait to replace the more expensive it will become. Gas is always rising in price. If you think it's expensive at the moment just wait a few years! There are some sectors saying that the price will DOUBLE within a few years. The price of an install remains relatively constant. There are grants available through the Green Deal and various other places..
          Find a grant / Take action / Home (England) - Energy Saving Trust England
          Info central heating grants
          You don't need to be on benefits for all of them.
          If you don't ask...
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