Al wrote:

I have an 8 year old Worcester Greenstar Heatslave 18/25 oil-fired boiler
which has been misbehaving lately. Whereas previously the pressure gauge
only moved over a very limited range during the course of day in which
heating and hot water were required, over the last few months that range
has got wider and wider, from zero first thing in the morning before it
fires up, to about 2.5 a few hours later. IIRC, if it gets to 3 it will
activate a pressure relief valve and dump water all over the floor, which
I'd really like to avoid obviously.
What's the most likely cause of the problem?

As others have said, its caused by insufficient expansion space for the
water. That said, unless your boiler was installed by a complete cowboy,
it shouldnt dump water on the floor. The pressure relief valve should be
plumbed in to carry the overflow into a drain or outside somewhere.

Tim


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