Baxi 80e Air in Primary Heat exchanger??

Discussion in 'Plumbers' Talk' started by rickypj, Nov 14, 2017.

  1. rickypj

    rickypj New Member

    Hi all,

    This one has had me scratching my head for a couple of days,

    The Boiler (baxi 80e) operates fine on the DHW side but once the CH is switched on it will run for a few seconds maybe a minute, LED's indicate temp reaching 80degC, emit a kettling sound, and switch off with no faults indicated. this cycle will repeat constantly. With this the boiler is not on long enough to heat the radiators. Pump is running and the 3way Valve operates as it should.

    I did a bit of research and found a way of clearing possible air locks/trapped air by stopping the pump whilst its running by jamming a screwdriver against its spindle to stop it and releasing it a few times. This initially seemed to do the trick as the kettling noise stopped and the Boiler ran for around 30 mins. (radiators were also all bled)
    Once the boiler switched back on with CH demand it returned to making the noise again and switching off cycling behaviour.

    I am sure it is due to air in the primary heat exchanger allowing the Primary circuit to boil or creating a loss of flow.

    Im confused though as the DHW seems to operate as it should. Even with the boiler emiting a noise it doesnt switch off and will run for as long DHW demand is on.

    any help would be great

    Thanks all Rick
  2. Dave does Gas

    Dave does Gas Well-Known Member

    Its not air trapped in the heat exchanger, If you had air trapped in the primary heat exchanger then you would have the same symptoms on the DHW side as well as its the water from the primary heat exchanger that heats the water in the plate to plate heat exchanger.
    Your symptoms are caused a little further on, Possibly weak/failing pump, or diverter valve not fully opening, or even a very dirty system or obstruction in the flow pipe.
    Hard to diagnose without being in front of it, but if you have any means to take the temperature of the flow pipe and note at what temp the noise stars that would be a start.
    If the flow gets excedingly hot at the time of noise first place to look is the pump.
  3. rickypj

    rickypj New Member

    thanks for your reply. I have changed the pump and bled the system today and the boiler is still rising up to temp on the led's (80degC) and cutting out after running for around 30-60 seconds then on to repeat the cycle after 2-3 mins. The flow out of the boiler is getting hot and there is still a whistle/boil/kettleing noise from the top of the unit/Primary heat exchanger area. The rads do begin to warm up and the return to the boiler also gets warm after a bit of time.

    Could the problem be the primary heat exchanger blocked/scaled up? or would a blocked heat exchanger cause things to not heat up quickly???
  4. The Teach

    The Teach Well-Known Member

    Dave does gas,has mentioned the diverter valve.One of the internal valves may not be opening or closing fully for radiator demand or there could be debris blocking an internal port its impossible to see with out taking it apart.service kit is available.

    Other checks,is there a filter in the return or heating isolation flow valve ? Remove the bulbous end cap facing you (drain down to that level first !) have a look.
    When the cap is off you can also see if the plastic handle isolation valve is actually fully open,worth looking in both heating isolation valves. If there is any debris sitting the the valve,pull it out.
    Are all the radiator valves open enough,worth checking the lockshield and other valve/trv is fully open on at least 2 radiators.

    Does not sound like an air issue,circulation yes :(
  5. The Teach

    The Teach Well-Known Member

    We dont know if you have a way of measuring temperature in different parts of your boiler or measuring thermistor resistance,your boiler is fixable :)

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