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central heating system continuous overflow

Postby jardov » Thu Dec 20, 2007 12:00 pm

We recently had a new boiler installed (replaced LPG with oil) - it's a Grant 160/200, apparently a 140/160 would have been sufficient but it wasnt available.

The problem is that ever since it's been installed the system has overflowed. It only overflows when the CH is on, and starts a few minutes after it's been turned on.

The speed of overflow is dependent on the pump speed, but even on it's lowest setting (1 of 3), the overflow drips constantly (it runs like a tap on setting 3).

The plumber has been back once but only emptied the header tank which did nothing but buy me a few days before it filled again.

Any ideas?


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Postby marrtin » Thu Dec 20, 2007 1:57 pm

If you mean the header tank is overflowing to outside the house, then either the ball valve in the header tank is weeping or the hot water cylinder heat exchanger has failed and water is transferring from the DHW side to the CH circuit.

Think you may find the boiler change is a red herring although disturbing the system may have caused the final failure. Was your system gravity fed before?

You need to confirm this is indeed the case before an undergoing an expensive repair.
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Postby htg engineer » Thu Dec 20, 2007 4:55 pm

was the position of the pump altered when the new boiler was installed ? it sounds like the pump is pumping water over into the header tank, could be the positioning of the pump to blame.
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