Pump on Cold Feed to Shower using Combi Boiler

theplural

I have a shower that uses a Combi-boiler for the hot feed and takes the cold from a storage tank in the attic.

I recently had the bathroom re-done and the shower pressure is now barely usable. Though it wasn't amazing before either.

We recently had a thermostatic mixer valve put in that was speced to work from 0.2 bar upwards but with this in place the pressure warbled as the valve and\or the boiler switched on and off every second.

We replaced the mixer with one that was speced from 0.1 bar upwards and the pressure warbling has stopped but the pressure is just not good enough.

The hot pressure is acceptable as the flow is fine when I turn it up to scorching, but at a lower temperature the pressure is low.

I'm thinking of getting a(different) plumber to advise but with the hope of him fitting a pump on the cold feed but am concerned about:

a) Fitting a pump to a shower using a combi boiler. I know it's not fitted to the hot pipe but maybe it can draw hot as it's pumping it through the same mixer? Too far-fetched?
b) As the hot pressure isn't spectacular either, maybe a pump on the cold would overpower the hot.
c) The freaking noise of a pump which, due to lack of anywhere else to put it, would have to be in the attic, beside the tank, and above the main bedroom.

I'm looking to rent out this house so maintenance\durability is also a concern.

Any tips, advice or sobering smacks across the face?

Combis are a mains fed appliance and if you have bad amins then a break tank with a pump is used to mimic a decent mains supply.

If hot water is pumped and your cold isn't would be a bad design, any mixing taps would have the hot over powering the cold.

In a ideal world you would have equal pressure for the cold and hot.

theplural

Thanks for the tip Gary.

My explanation above may have been even more mangled than my new pipework though.

The mains pressure, and thus the hot feed to the shower, is acceptable. The cold feed from the storage tank in the attic is the problem as far as I can tell.

I'm hoping to fix this without any major replumbing as I've just redecorated.

If hot water is pumped and your cold isn't would be a bad design, any mixing taps would have the hot over powering the cold.

Thanks, this probably applies for me in the reverse so. If I put a pump on my cold then it could overpower my hot in the sink mixer and in the thermostatic shower.
If I got a low-pressure pump, such as 1.5 bar one, on the cold do you think this could be low enough?

LIFFY FISHING

The only shower that will work properly off a combi boiler is a pressure balancing shower valve, a thermostatic valve wont function properly because of pressure loss ratio, what type and make of shower valve have you installed?

theplural

theplural wrote: »

Thanks, this probably applies for me in the reverse so. If I put a pump on my cold then it could overpower my hot in the sink mixer and in the thermostatic shower.
If I got a low-pressure pump, such as 1.5 bar one, on the cold do you think this could be low enough?

in a ideal world you would have equal pressure on your hot and cold, I have found problems with mixing taps when they allow the pressure to equalise when one side is higher than the other.

K.Flyer

theplural wrote: »

Thanks for the tip Gary.

My explanation above may have been even more mangled than my new pipework though.

The mains pressure, and thus the hot feed to the shower, is acceptable. The cold feed from the storage tank in the attic is the problem as far as I can tell.

I'm hoping to fix this without any major replumbing as I've just redecorated.



Thanks, this probably applies for me in the reverse so. If I put a pump on my cold then it could overpower my hot in the sink mixer and in the thermostatic shower.
If I got a low-pressure pump, such as 1.5 bar one, on the cold do you think this could be low enough?

By putting a pump on the cold supply you could invariably end up flipping the same problem if your pump is more powerfull than your mains.
Depending on what pipework has been left behind it may be possible to rectify the problem without too much disruption, but you should prepare for the worst case.
It still baffles me how people can get installing a combi boiler so wrong, expecting mains water and stored water to be of equal pressure.