Only pump the hot water?

I have a thermostatic mixer shower that is fed from mains cold water and a gravity-fed hot tank. The cold cistern is communal (block of flats) and about 18" above the shower head. Needless to say it only gives a trickle out of the shower.......the hot water in the kitchen is pretty pathetic as well (yes, I've seen the post about mains-pressure suitable taps).

Can I fit a pump on the outlet from the hot tank to help equalise the pressures?

All cold water in the flat is mains-fed and any new pipework would have to be surface-mounted (no roof void and concrete floors).....I'd rather not do anything too messy right now since there are tenants in situ and I can't afford a long void period and major re-jigging of the plumbing.

Well yes and no!!!

You CAN fit a shower pump to the hot water outlet and ideally this should be specified to give a pressure as close to the mains pressure are you can. You may well find that the pump will only start if the hot tap is turned on first but that would not be much of a disadvantage.

BUT doing so will give rise to serious risk of malfunction and contravention of the water Regulations. You can minimise this risk by ensuring that a double non return valve is placed in the mains feed to each outlet where hot water could be mixed, eg combined spout taps or mixers of any kind. Ideally a non return valve should be on the hot as well to get a little closer to meeting the Water Regs.

Really I would that only a Water Regulations qualified plumber is used to advise. These are about one plumber in a hundred!

Tony Glazier