Shower pump not needed?

[Alan (BigAl)]

Am I right in saying that with a combination boiler with no header tank, with direct connection to the mains water, that is is inappropriate to use a booster pump?

I am planning to redo the bathroom, to include a separate shower unit. I was planning to use a thermostatic controlled shower unit to blend hot and cold feeds.

Presently we have a shower over the bath, with a combined tap/shower without any temperature regulation. This is very hard to adjust and both the hot and cold flows seem to be quite restricted. However, the old tap/shower unit may well have got a bit of scale or gunge, but I was expecting more vigorous flow, and suspected that the low pressure might be detrimental with a new shower too.

I just did a pressure test, and have 32 psi dead ended pressure. This was on the ground floor, so 3 metres higher (bathroom upstairs) it will be ~5 psi lower.

That seems a bit lower than I expected, but I have no real data to compare it with.

Checking the installation instructions from a shower plucked at random from 'tinterweb, it seems that it would be ok with pressures of 1 bar, or even lower if the flow restrictors are removed.

Am I worrying needlessly? Am I missing something? Does anyone have any advice for me please?

Cheers Alan

[dennis]

You usually have plenty of pressure with a combi. That doesn't mean you have plenty of flow. The combi can only heat a limited number of litres per minute. Typically you can get about 8-15 litres per minute. This may be enough if you have a suitable shower head. Don't expect it to be enough if you imagine having a 30cm square soaker hanging from the ceiling. Fit a thermostatic mixer or you will find the temp changes when someone turns a tap on, etc.

[DavidM]

Before installing a shower in my son's bathroom a couple of years ago (albeit one over a bath) I lashed up a connection using garden hose between the hot water feed from the combi and his new shower head, temporarily fixed at roughly the finished height with bucket underneath, just to check the flow/pressure. It seemed ok.

Final installation had hot and cold feed into a thermostatic mixer, thence to normal shower head on flexible hose. Still working ok and no problems with other taps being turned on/off.

As said above, don't expect a waterfall shower through a combi!

[TMC]

but in the meantime

for a combi boiler system use a pressure balanced mixer

traditional showers have a temperature balanced mixer which needs the incoming supply of both hot and cold to be the same pressure the cold feed would come from the output of the header tank for the hot water system not from the incoming mains

A pressure balanced shower assumes a constant hot water temperature which one normally gets from a combi boiler and balances the differential in pressure to get the required temperature

I have had a mira one fitted for 18 years without problem other than replacing the shower head once and hose twice

I do not see how a booster pump can work with fixed volume output from the boiler

Regards

Regards

[fred]

In article , TMC writes

Yep, that's right, flow will be limited by the heat output of the boiler.

Worth noting too that you're not allowed to pump from the mains (either on the cold feed or via the combi), only from a tank fed system. It's to do with the risk of causing negative pressure in the mains and sucking in impurities or bacteria.

[MuddyMike]

I am confused, I thought combi boilers did away with the loft tank? Don't both hot and cold come at mains pressure?

Mike

[TMC]

[MuddyMike]

The flow may be restricted but surely the pressure is the same?

Mike

[Alan (BigAl)]

Thanks all for the input. I think that I will use one of these : -

summat similar.

Now - if I mount it into a corner with two solid brick walls, how best to pipe up to it? Is it usual to create a false wall and tile it, or cut a channel for the pipes?

Sorry for the stupid questions, but this is one of the few jobs around the house that I have not yet tried to do.

[dennis]

or summat similar.

Its quite common to see stainless steel pipe running down the walls to a surface mounted valve in those situations.

No such thing as a stupid question, only stupid answers.

[Roger Mills]

or summat similar.

You'll probably want to tile it, either way. In your situation, I'd cut a channel in the brickwork and use copper pipes - with compression to FI elbows at the appropriate place for connecting the shower.

[MuddyMike]

or summat similar.

I found that cutting a plywood template with two holes to keep the pipe ends in the right place and at the correct distance apart was a great help when I fitted a similar shower with the pipes embedded into chases in a brick wall.

Mike