Electric shower has no pressure or a weak flow

What it usually means

The first thing to understand about a feeble electric shower is that the shower may be doing it on purpose. An electric shower heats water as it passes, so the hotter you want it the slower the water has to go, and every unit sold in the UK has either a flow control you set by hand or, on the thermostatic models, a motorised valve that sets it for you. In January, when the mains arrives at six degrees, an 8.5 kilowatt shower can only produce a comfortable temperature at a flow that feels like a dribble, and turning the temperature up makes the flow worse, not better. A shower that is weak in winter and fine in summer is not faulty. The all-brands page on a shower that is not hot enough explains the arithmetic, and the honest fix is a higher kilowatt unit, which is an electrician’s job because of the cable and the breaker it needs.

Once that is ruled out, the flow is being lost somewhere between the mains and the spray plate, and the order to check is from the cheap end. The handset first: limescale in the spray plate nozzles is the single commonest cause of a weak shower, it builds slowly enough that nobody notices, and it also raises the temperature and trips the over-temperature protection because the restricted outlet backs water up in the heater. Redring say to rub the rubber nozzles or soak the plate in descaler; other makers say the same in their own words. Then the hose, which can be kinked behind the riser rail or collapsed internally. Then the servicing valve on the cold feed, usually a slotted quarter-turn isolator near the shower or under the bath, which a plumber or a previous owner may have left half shut. Then the mains itself, tested at a cold tap fed from the same pipe: a weak tap means the pressure at the house is the problem, and no shower can fix that.

The showers that do have a display or indicator will tell you when the supply is the issue rather than the head. Triton light a low pressure indicator, Bristan show LP, the Redring Selectronic Advanced shows LP with its Start/Stop light flashing slowly when the supply drops below two litres a minute, and Mira’s code A groups no supply, low pressure and a blockage in the outlet together. Those pages give each brand’s exact wording. On the older rotary-dial showers there is no code, and low pressure shows as the protection working instead: a shower that cuts its elements and runs cold rather than heat a trickle, or one that cycles between hot and cold as the stabiliser valve hunts.

Behind the cover there are two more causes, and both are competent-person work. The inlet filter, a small strainer where the pipe enters, silts up in hard water areas and after mains work in the street, and manufacturers describe cleaning it as a job for a competent person because the fitting is next to the terminal block. And the flow valve or stabiliser itself can stick partly closed, which on a thermostatic shower shows as a flow the buttons cannot change. An old shower that has been weak for years on a good mains, with a clean head and an open valve, usually has one of those two, and on a unit of that age the price of the visit is weighed against a new shower, which would also allow a higher rating and a better winter flow.