bath/shower mixer won't work

[nigel davies]

Have just fitted a bath/shower mixer. However, the shower bit only seems to work with the cold tap and not the hot! Anyone any advice?

[Ed Sirett]

Bet you have a tank fed system which is at the same level as the bathroom. Likely a 70s/80s flat or refurbished then.

[Christian McArdle]

You may have a tap that isn't suitable for your hot water system. In particular, there is likely to be a substantial pressure difference between hot and cold supplies. Your cold supply is probably at mains pressure (v. high), whilst the hot supply is tank fed (low pressure). When the two mix in the chamber, the cold may push the hot back up the pipe. This is more likely to happen on the shower than the bath because the shower head is high up. If the header tank is on the loft floor above, this substantially reduces the hot pressure, making the effect more likely.

If you have a combination gravity cylinder on the same floor, you may even find that you have no head at all, as the header tank will only be around head height.

Solutions:

1. Replace hot water system with mains pressure.
2. Install low/-ve head shower pump.
3. Learn to enjoy baths.

Christian.

[Lobster]

More info needed before anybody can respond helpfully!

Is this a mixer tap where you switch between bath taps and showerhead with a lever?

Do you mean that if the hot tap is running on its own, nothing comes out of the shower head at all, but it does come out of the tap? And that cold on its own is OK? Would be unusual...

Or is the problem that you just can't get a decent mixture of hot and cold? Which would imply the cold is at much higher pressure than the hot and is overwhelming it, and you probably have the wrong type of mixer valve.

What sort of system do you have - what type of boiler is it; and do you have a hot water cylinder and/or cold water tank in the house?

David