Blocked system or Heat Exchanger/Pump

[Kidda]

Hi all,

Found this site and hope someone more qualified than myself can help. My boiler is making a banging noise and reaching the temperature set on the boiler within approximately 10 seconds at which point it bangs loudly and the burners shut off. Hot water is leaving the flow and I feel the pump is working, however little hot water is returning on the return. To compound matters its an unvented system run through a Vokera mynute 28e on (wait for it) a one pipe system. Up until recently the system ran like a dream for 6 years with only one previous problem, on what is a fairly large 3 storey house. About two years ago the same problem occured and the heat exchanger was taken out, cleaned with all sorts and put back, this seemed to cure the problem. We are now on a BG homecare plan and they seem to think it's a system blockage. At a chargable rate they have now put Fernox F3 into the system and will be leaving it for 2 weeks before flushing through, the system is to be left running permanently on and the pipes serving the rads are just above cold, therefore water appears to be circulting just about, however the burners still turn off within seconds, as the required temperature has been achieved. For information they drained the system fully before re-filling and putting in a F3, interestingly the water they drained off appeared to be crystal clear.

Strange one but BG didn't check the pump physically (as it is my understanding that the motor can be running without the pump turning), furthermore they chose to ignore me when I advised that last time a similar problem occured the heat exchanger was blocked. Could it be that water is not moving through the exchanger fast enough due to a blockage, therefore water is reaching temperature quickly and the system is turning off ? not to mention the banging. Or could the pump be running intermittantly ?


Sorry for the long winded explanation, any opinions would be appreciated for me to poise to BG.

Cheers,

Kidda.

 

[dougal]

i would first double check, making sure there is no air in system, then check pump put on max speed and undo spindle screw place little container under small amount water put screw driver in see if pump shaft stops if does with little force pump may be weak. if pump not running at all you need check 230v at pump. if pumps fine there will be blockage by cleaning may not solve problem.

 

[Js58gas]

As dougal said check the pump first as this would be the easiest. If the pump is ok there must be a restriction in the system , the problem is trying to clear this, normally I would say powerflush the system but with a one pipe the machine wizzes past the rad not cleaning the whole system . So I would manually take the rads of and clean them then I would add some fernox f5 and powerflush the pipework and boiler this should stop this from happening in another 3 years.

 

[Kidda]

Many thanks for responses.