The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 11 replies
  • Subscribers 31 subscribers
  • Views 1047 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Combi Boiler.

Zoomup
Old Alpha HE CB 25.


 I have checked the pump, all o.k. Fan o.k. New hot water diaphragm- switch working o.k.

Circuit board o.k. Boiler tries to light but shuts off after a few seconds. No hot water. No central heating.


The strange thing is that when a hot tap is opened the central heating water pressure goes down. Is this a heat exchanger problem?


Thanks,


Z.
  • 0
    Flue pressure switch? (confirms to the circuit board that the fan is running)

      - Andy.
  • 0
    Sounds like no gas if the ignition spark is present.
  • 0
    I hate those things. Noisy and too many components! I shall stick with my floor-mounted cast iron ones.


    (How do you put things on top of a wall-mounted combi to dry them out?)
  • 0
    Pressure drop seems strange - partly blocked heat exchanger? If so, I'd expect some kind of overtemp alarm. What is the boiler locking out on? My old Baxi posed a pig of a problem with the what I thought was the pump - seems the pump isn't a pump in the conventional sense, but merely a water circulater which creates no pressure of it's own. A new pump did the trick though. Seems the old one wasn't circulating at the correct rate. Another thing to check might be the DHW and CH temp sensors on the pipework inside the boiler - a straight continuity check will tell you if things aren't right.
  • 0
    whjohnson:

    Pressure drop seems strange - partly blocked heat exchanger? If so, I'd expect some kind of overtemp alarm. What is the boiler locking out on? My old Baxi posed a pig of a problem with the what I thought was the pump - seems the pump isn't a pump in the conventional sense, but merely a water circulater which creates no pressure of it's own. A new pump did the trick though. Seems the old one wasn't circulating at the correct rate. Another thing to check might be the DHW and CH temp sensors on the pipework inside the boiler - a straight continuity check will tell you if things aren't right.


    I am suspecting a wrongly fitted new diaphragm/needle for the D.H.W. in the diverter valve, or a leak in the heat exchanger that is allowing the sealed heating side water to leak into the D.H.W. system, thus allowing a pressure drop in the heating circuit when a hot tap is opened.


    All observations welcomed.


    Z.


  • 0
    The observed pressure drop might be normal - it all depends on the design and the position of the gauge relative to the pump etc. There's got to be a pressure difference to have a flow (like Ohm's law, there's got to be a voltage difference if there's a current flow). I'd only worry if you know it's not normal for that make/model of boiler, or if the pressure goes down but doesn't recover again when the pump stops.


    Usually the tap water side would be at a higher pressure than the sealed CH side anyway (otherwise filling the system from a simple loop wouldn't work...).


       - Andy.
  • 0
    AJJewsbury:

    The observed pressure drop might be normal - it all depends on the design and the position of the gauge relative to the pump etc. There's got to be a pressure difference to have a flow (like Ohm's law, there's got to be a voltage difference if there's a current flow). I'd only worry if you know it's not normal for that make/model of boiler, or if the pressure goes down but doesn't recover again when the pump stops.


    Usually the tap water side would be at a higher pressure than the sealed CH side anyway (otherwise filling the system from a simple loop wouldn't work...).


       - Andy.


    When the hot tap is opened at the sink, the closed heating (radiator) system de-pressurises to zero.


    Z.


  • 0
    It sounds to me you need the services of  a Gas Safe heating engineer.


    David
  • 0
    davidwalker2:

    It sounds to me you need the services of  a Gas Safe heating engineer.


    David


    Yes, one will be employed to check the gas parts and to give the boiler a final signing off. I am just looking at the plumbing issues at present for friends.


    Z.


  • 0
    When the hot tap is opened at the sink, the closed heating (radiator) system de-pressurises to zero.

    And stays at zero when the tap is closed again?


    That's odd - even with the hot tap open the DHW pressure should be significantly higher than zero.


    Is there any sign of water escaping from the pressure relief valve? (usually through a copper pipe poking through the outside wall) - if the expansion vessel has failed a small increase in pressure can result in the PRV opening and so dropping the pressure. Of course the PRV should close again as soon as the pressure drops towards normal - but they're often a bit sticky and don't always reclose when they should.


       - Andy.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines