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Combi Boiler.

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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.
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  • 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.


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  • 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.


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