can i put a shower pump on a combi boiler?

Postby muppet1967 » Sun Nov 23, 2008 8:48 pm

I've just put a triton thermostatic shower in and i'm running it off a baxi 105e combi boiler but the hot water pressure is not too good. I think the problem is that the boiler is quite a distance form the mains and the shower is quite a distance from the boiler. Can i put a pump on the shower even though its a combi boiler, if so which one would you recommend?
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Simply Build It

Postby chris_on_tour2002 » Sun Nov 23, 2008 11:20 pm

i wouldn't have thought that the distance of your boiler and shower from the mains/eachother would be the cause, unless you happen to have very low mains pressure.

you cannot fit a pump anywhere on a combi system as they operate at mains pressure. check to ensure that your shower is compatible with combi systems. if not then you will need to change it for one that is. check the output and flow rate of your boiler and purchase a new shower to suit.
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Postby muppet1967 » Mon Nov 24, 2008 5:07 pm

The flow rates are @25c rise--17.8 l/min
@35c rise--12.7 l/min
I removed the shower unit then turned on the iso valves, the cold shot out and hit the glass, the hot just trickled out so the problem is a flow problem. When you turn on the hot it wont fired up the boiler yet the bath and basin are no problem, help please there must be something. Are you sure a small pump cant be used?
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Postby chris_on_tour2002 » Mon Nov 24, 2008 11:04 pm

i can certainly assure you that a pump cannot be used on a combi system for several reasons:

i) many pumps cannot handle mains pressure
ii) no tank/reservoir so the pump has no stored water to draw from
iii) you will pull water away from your combi faster than it can be heated
iv) the water authorities forbid the installation of a pump on a mains circuit. to do so is illegal.

if the shower unit is completely removed and you are still getting poor flow directly from the pipe it suggests a blockage in the pipe or faulty plumbing. you need to trace the pipework all the way back to the boiler and check it all along the way.
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Postby htg engineer » Tue Nov 25, 2008 12:07 pm

What's the flow rate like from the taps ?

If they're the same - it could be that the plate heat-ex is full of limescale.

htg engineer
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Postby plumbbob » Tue Nov 25, 2008 3:56 pm

Check the inline pipework and shower unit for any inline filters. These strainers are easily blocked with debris during installation.

Combi's should give excellent showers so the fault must be with the pipework.

What model of shower is it?

Do you get good hot water flow from the sink and basin taps?

As Chris and Htg say, absolutely no pump can be fitted - Sorry.
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Postby muppet1967 » Tue Nov 25, 2008 7:08 pm

Yes i get the "no pump" bit, thinking about it its probably the plumbing. There's a lot of 90 degree angles, the iso valve is not full bore and i put a flexi pipe on the last bit of pipe work which is also small bore so i think i'll change these and re-route the pipe work to eliminate the resistance. Thanks guys i'll let you in a couple of weeks when i get round to it.
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