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Newbie to kitchen bashing DIY - we are in a bungalow, so tank-fed hot water is slow at the best of times! If hot and cold water are mixed through the kitchen tap, the mains pressure seems to force its way back up the hot feed, so when you want just hot water, it takes an age to come through again! My question is: is there a small, inline negative booster pump available that can be fitted just before the tap under the sink and would fitting an inline non-return valve also help with the problem? Single impeller shower pumps seem to be too big/powerful for what I need. All fittings are copper and 15mm.
Thanks for reading this missive! :)

If the tap has a combined flow, and one side is fitted to a low pressure supply, a one way valve should have been fitted during installation. The trouble with these valves though is they usually reduce the flow even more, and if the pressure is very low, can stop it altogether.

Fitting a pump under the sink may add another problem to your woes. If a bathroom hot tap is used at the same time, it may allow air to be drawn into the hot flow and cause an airlock. Far better to fit the pump next to the header tank or DHW cylinder and pump to all hot taps. Then a standard single impeller pump would suffice.