I need to replace my existing boiler with a new condensing boiler. As I understand it, a system boiler has built in pump and expansion vessel, whereas a regular boiler doesn't. My current CH system has a pump in the airing cupboard, but I do not think there is an expansion tank in the loft. Now I'm slightly confused because I'm not sure if the current boiler has a built-in expansion vessel. So I'm looking for clarification on whether I need a regular or system boiler.
Thanks.
Just another note to this - assume it's a regular condensing boiler I need, then the one I'm looking at is the Worcester Greenstar 24Ri. This is for a 4 bed house with 2 bathrooms, and 15 rads.
Correct (with exceptions)
When the heating is on the water expands and the increased volume has to go somewhere. You have an open vented system so the level the header tank will go up a bit. The alternative - now generally preferred, and required with many boilers - is a sealed system, where the expansion is taken up by the expansion vessel: in simple terms it's got a large balloon in it which compresses as the water expands.
Check out the sealed system FAQ at
We had one of these installed just before Christmas. Four bedrooms, two toilets, one shower room and 17 radiators. It copes extremely well and has the house and DHW up to temperature in no time at all. We kept the rest of the vented system with no alterations other than the location of the pump: the hot water cylinder remains in the airing cupboard and the expansion tank in the loft.
The only disappointment is the ugly black plastic flue protruding from the wall. Pity Worcester Bosch couldn't have spent a few more pence on something a little more pleasing to the eye.
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