Cold showers come from three different worlds: the shower valve itself, the water system feeding it, and the way the two were matched when the bathroom was fitted. That is why generic advice rarely helps. Before you spend anything, work out which type of shower you have and what happens in each of the situations below. In most homes the answer turns out to be a worn cartridge, a scaled valve or a shower that was never suited to the system it was plumbed into.
Identify what you have first
An electric shower has a boxy unit on the wall with its own cable and heats cold mains water as it passes through. A mixer shower blends existing hot and cold, either from a valve on the wall or from a bath tap. A power shower is a mixer with an integral pump, only used on gravity fed systems. Then look at your heating: a combi boiler with no cylinder, an unvented cylinder such as a Megaflo, or an older gravity system with a cold tank in the loft and a copper cylinder in the airing cupboard.
Symptom, it goes cold when another tap runs
Classic pressure imbalance. A manual mixer holds a fixed ratio, so when someone runs the kitchen tap the cold side pressure drops and the blend swings hot, or the reverse. The proper fix is a thermostatic mixer valve, which reacts to the change and holds temperature. This is also a safety issue in homes with children or older people, and it is why we fit thermostatic valves as standard.
Symptom, it starts hot then goes cold
- Combi boiler cycling. If the flow rate through the shower is below the boiler's minimum, the burner keeps dropping out. A flow restrictor in the head or a partly closed isolator is often to blame.
- Cylinder run out. On a gravity or unvented cylinder, an earlier bath may have used the stored hot water. Recovery takes time, and no shower valve can fix an empty cylinder.
- Scaled cartridge. Limescale on the thermostatic element makes it slow and jumpy, so the temperature hunts.
Symptom, an electric shower is never really hot
Electric showers apply a fixed heat rise. A 8.5kW unit will raise incoming water by a certain number of degrees, so in January, when the mains is close to five degrees, the same setting feels far cooler than it did in July. Turning the flow down gives the element more time on the water and raises the temperature. If it is cold rather than just cool, suspect a failed heating element, a tripped thermal cut out or, in hard water areas, a scaled heater can.
Symptom, it went cold suddenly and stayed cold
Sudden total failure points at something mechanical: a failed thermostatic cartridge, a stuck check valve, an airlock in the hot feed or a closed isolating valve that has been knocked. On a combi, no hot water anywhere in the house is a boiler problem rather than a shower problem, and that needs a Gas Safe registered engineer.
Safe checks you can do
- Run the hot tap at the basin. If that is also cool, the fault is upstream of the shower.
- Unscrew the shower head and clean the outlet plate in descaler. Restricted heads change flow and temperature.
- Check the isolating valves on the shower feeds are fully open.
- On an electric shower, check the pull cord switch and the breaker, and reset the unit's cut out if it has one.
- Note whether the problem is worse when other water is being used, which separates pressure faults from heating faults.
Anything involving the boiler, the unvented cylinder or the electrical supply to a shower needs the right registered trade, and we will say so rather than have a go.
Getting the shower matched to the system
A lot of the cold shower calls we get are not faults at all. They are a shower that was never suitable for the house: a power shower on a mains fed combi, a big rain head on a low pressure gravity system, or a thermostatic valve fed by pipework that is too small. Getting this right at design stage is a large part of what a bathroom fitter is for, and it costs nothing extra to specify correctly the first time.
Talk to a local fitter
We fit and replace showers, valves and full bathrooms across Stoke-on-Trent and the surrounding towns. Describe the symptom on the enquiry form, tell us your boiler type if you know it, and we will tell you what is likely and what it would cost. See also our bathroom fitting service.
Common questions
Why does my shower go cold when a tap is used elsewhere?
That is a pressure balance problem. A non thermostatic mixer cannot compensate when flow is stolen from one side, so the blend swings. A thermostatic valve is designed to stop exactly this.
My electric shower is lukewarm in winter, is it faulty?
Not necessarily. Electric showers heat incoming mains water by a fixed number of degrees, and mains water is colder in winter. Reducing the flow rate raises the temperature.
Why does it run hot then cold after a minute?
Usually a scaled or sticking thermostatic cartridge, or a combi boiler cycling because the flow rate is below its minimum. Both are common and both are fixable.
Could the shower be drawing from a cold tank?
On older gravity systems yes, and if the cylinder has been drained by earlier use you get a cold shower until it reheats. Recovery time is the giveaway.
Is a new valve worth it or should the whole shower be replaced?
If the pipework and enclosure are sound, a new thermostatic valve or cartridge usually solves it. Replace the lot only when the fittings are corroded or you are changing the layout anyway.