Help! No hot water pressure!

[lau89]

Hi,

I have recently replaced my standard bath taps for a thermostatic bath/shower mixer.
There has never been the greatest hot water pressure in this house, however after the new mixer was put on, it seemed to be reduced to just a dribble. (We had to change the gate valve as well during the fitting of the mixer as it jammed...) Also, we noticed that the overflow pipe was leaking (which it had never done before).
To fix the overflow pipe and possibly increase the water pressure, we fitted a pressure reducing vavle. This has helped the overflow situation but has done absolutely nothing towards helping the water pressure.

The hot water is gravity fed to a cylinder in the airing cupboard (in bathroom).
The cold water is mains fed.

The house isn't that old - was built in 90's, so we're hoping that there isn't a problem with the pipework.

Any help/advice would be appreciated!!

[feltham]

you should have equal pressure from both taps as the cold will push the hot back into the tank and then your overflow will run.
you could run another outlet from your tank to get equal pressure to your cold or fitting a unvented hot water system to get mains pressure hot

[PLUMB111]

You say you have a Gravity System, are you sure that you have been sold the correct taps as it may be that your new taps are only suitable for HIGH PRESSURE.

This would restrict the flow.

And your system is low pressure.

[Bernie2]

Hmm!

I would agree seems a bit odd!

The hot will be low pressure if its gravity fed, but the cold high pressure.

However if you have a prv on the and govern it down to the same pressure as the hot then one would assume it should work and both pressures being equal the cold should not overcome the hot as it seems to have been doing.

But as has been said, some mixers are high pressure and so the gravity hot water pressure simply may not open it enough to allow hot water through, but the cold being high pressure does.

[Mushybees]

PLUMB111 is probably right. Fewer and fewer taps are appropriate for low pressure systems these days.
Instead of a pressure reducing valve you should fit check valves on the supplies. This will stop the mains cold forcing it's way into the hot pipework.
If you do replace the taps it's still important you fit these.

[Bernie2]

Hmm!

Why did they do away with bi-flow mixers? Keeping the water streams separated stopped a lot of problems.