DHW PROBLEMS


Postby wiggy » Mon Jan 14, 2008 9:31 pm

I have a fully pumped open vented heating system. The boiler is a Baxi solo wm 50/4 rs with a grundfoss 15/50 pump and a honeywell 3 way mid position valve. When the heating is called for there is no problem, if the heating and water are both called for (or the dhw on its own) after about an hour the system starts making loud noises through the vent pipe into the expansion tank which in turn gets hot. When I turn the water off at the timer I continue to get the noise and the heating wont work, I then have to wait a while and bleed the radiator in the bathroom (nearest the pump) and the 2 bleed vents either side of the pump then turn the heating back on and it will work. At present the heating is working perfectly but I am having to heat the water with the electric imersion heater. I think that the problem lies in the dhw circuit but I dont know what. I have just fitted a new 3 way valve and new pump but the problem persists. Any help please - wiggy.
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Postby rosebery » Tue Jan 15, 2008 10:22 am

It sounds as if you are drawing air into the system somewhere which points to excessive negative pressure in the pipework. This has nothing to do with the static head pressure BTW - it's related to the pump. But then it seems to be changing over to an excessive positive pressure situation resulting in pumping over.

Is the pump in the flow or the return?

Where is the pump situated relative to the cold feed and the vent?

In any case it's very difficult to do remote diagnosis being unable to see it and your best solution might be to close this thread and get someone in to have a look.

Would be interested to know the result.

Cheers
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Postby wiggy » Tue Jan 15, 2008 9:39 pm

Looking at the pump it is on the flow side and the boiler is on the return.
The cold feed to the pump drops down from the expansion tank 3mtrs above in the loft to a 'T' piece a pipe branches off from the 'T' piece to the bottom of the pump, the feed pipe continues under the floor boards(this becomes the return from the boiler). Also the cold water feed pipe from the expansion tank is also the open vent, which I cannot quite understand. Hope this makes sense.
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Postby wiggy » Wed Jan 23, 2008 11:44 am

fitted new thermostat to boiler and thermocouple this seems to have cured the problem
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