Combi boiler or not ??

24 Dec 2003
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United Kingdom
As part of a kitchen upgrade, we are considering upgrading our central heating system. We are aware of some of the problems of combi-boilers but would welcome the increased space and lower heating bills. We live in a large, old maisonette so have quite a lot of bedrooms to heat and 2 bathrooms. Would a large combi boiler such as Worcester Highflow 400 cut the mustard and would we have to get all the plumbing in the flat re-done to allow for the higher water pressures ?
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Normal automatic answer for 2 bathrooms is Don't have a combi. The store would help but with 2 showers or a shower and a bath running it would be empty in minutes, but so would anything other than a very big store of hot water. THAT is if you have enough water pressure and flow from the incoming mains. Conversion flats often share a 1/2" mains pipe which is pathetic.

If you got the highest output combi you'd get 16l/min. If that could be evenly shared between 2 showers they would both be ok (electric shower is only 4l/min) but you would notice the difference. And if someone ran a hot kitchen tap the showers could virtually stop.
An electric shower does of course give you a backup for when the combi fails.

I do know people with 2 or 3 showers off a storage combi - they take very short showers and have learned to live with what they have. It's a compromise.

Any combi has enough output for a 2 bed flat, though they give no CH while the HW is on.
We are aware of some of the problems of combi-boilers but would welcome the increased space and lower heating bills

Where did you get this information? A recent housing study found there was no substance to the claims made by manufacturers that combis are cheaper to run. In fact, for the heating it will be less economical as the boiler has to be way overzized so it can deliver the hot water fast enough.

If you are running showers, think of 12l/min (6l/min absolute minimum) each. Baths take 12l/min from each tap. You will probably exceed the supply flow. all this and someone wants a tap on elsewhere, or a toilet.

But then some people are happy with them, er...service guys?
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A conventional system with the correct controls can be just as efficient!!

It will also sort out the mare that sometimes is; low H/W pressure on a combi.

Provided you have enough Head ;)

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