Combi or What?


29 Jul 2008
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United Kingdom
Have read a few posts where people have suggested that a combi may not be the best choice in a new boiler - I guess that this depends on useage, etc.

I will shortly be having some major work carried out which will include moving the position of the old combi but fitting a new condensing combi in the garage.

Haven't got to the point of asking the plumber/contractor for their suggestions yet, but is there an alternative/better choice than a condensing combi?

I want to locate it in the garage, which means that extending the existing pipework is not extensive. The house (once complete) will be a four bed, single bathroom (with bath and separate shower which is currently electric) - two of us and two young boys, which wont stay young for long, so useage will only go up!

any suggestions?
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Is the shower going to stay electric?

If so and if space is at a premium keep to a combi, but get at least a 30Kw, preferably a 35Kw +.

If shower is changing to come off new combi, then look at the Vaillant Ecotec Plus 937. Bit of a lump on the wall, but then it will be in the garage.

Get your cold mains flow and pressure checked first though.
I installed a Worcester Bosch greenstar 40 CDI combi about four years ago. This was the biggest "cheap" combi around at the time and it runs on a standard gas meter.

I have had no problems with it until recently but I expect that the diverter valve started malfunctioning about four weeks ago.

In my house, you get a crap shower when the water is being used for other purposes - I suspect this to be partly due to long pipe runs, and resistance in the thermostatic shower mixer. (My cold supply gives 18-20 litres/minute at the kitchen sink and 4 bar at the washing machine connection).

I installed the boiler in the loft, which is a great space saver but has the disadvantage of long pipe runs for the hot water. Thus it takes over a minute at the kitchen sink to get hot water. When I eventually get a kitchen extension I will move the boiler into the kitchen as close to the sink as possible. If you use 22mm pipe for the showers you will get better flow rate but it takes longer for the hot water to come through.
If you use 22mm pipe for the showers you will get better flow rate but it takes longer for the hot water to come through.

That would be very bad advice for virtually all normal combi installations unless the incoming mains water pressure is less than 0.6 Bar.

Even then a pumped supply would be the solution.

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Are you saying using 22mm is bad?

Doesn't it depend on how far the pipe has to go?

I am saying exactly that!

With mains water pressures a 15 mm pipe can go a very long way indeed!

In my mother's case, she was on 1000m of 15 mm water supply pipe but I agree the flow rate was only 4 li/min.


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