Why does my electric shower go cold or cut out?
Why an electric shower runs cold after a few minutes or shuts down entirely, which causes you can safely check, and the point at which it becomes an electrician's job.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 4 min
- Safety
- restricted
Short answer
An electric shower that goes cold mid-shower has almost always tripped its thermal cut-out, and the usual reason is restricted flow through a scaled head or a blocked inlet filter. Clean both first. A shower that cuts out completely and will not restart, or that trips the breaker, is an electrical fault — stop and call an electrician.
An electric shower heats mains cold water as it passes through, so its temperature depends entirely on how fast the water is moving. Anything that slows the flow makes the element overheat, and a thermal cut-out shuts it down to protect it. That is why the vast majority of 'cold shower' complaints turn out to be limescale rather than a failed unit.
Safety
What you'll need
- Descaler or white vinegar
- A small brush and an old toothbrush
- A bowl or bag and a cloth
Step by step
- Turn the shower off at the pull cord before touching anything.The isolator is usually a ceiling pull cord outside or inside the bathroom door. Leave it off while you work on the water side.
- Note the pattern before you start.Cold after two minutes every time points at overheating and flow. Cold immediately, or dead with no lights, points at electrics. The two have completely different answers.
- Descale the shower head.Unscrew it, soak it in descaler or white vinegar, and rub the nozzles with a thumb. A scaled head is the single most common cause of a shower that heats then cuts out.
- Check the hose for kinks and scale.Straighten it out and run water through it off the head. A hose that has been coiled tightly on a rail for years narrows internally.
- Clean the inlet filter.Most electric showers have a small gauze filter where the cold supply enters. Turn off the shower's isolating valve, undo the inlet nut and lift the gauze out. Grit and scale collect there and starve the unit.
- Confirm the water supply is fully open.The isolating valve on the supply and the house stopcock both need to be fully open. A stopcock nudged closed while working under a sink will do exactly this.
- Turn the temperature control down, not up.On many units, winter settings and high heat settings reduce flow to gain temperature. Dropping to a lower power setting can stop the cut-out triggering.
- Test it with the head removed.Run the shower with the head off the hose. If it now stays hot, the restriction was in the head. If it still cuts out, the restriction is upstream or the unit is failing.
- Stop at the casing.If the water side is clear and it still cuts out, or if it trips the breaker, has burning smells, or will not power up, it is an electrical fault. Leave the shower isolated and get an electrician.
Tips
- Descale the head every few months in a hard water area — it is the whole maintenance regime for an electric shower.
- A shower that trips the breaker or smells hot is never a plumbing problem. Isolate it and stop.
- Note whether it also happens when the cold tap is running elsewhere — that suggests pressure rather than the unit.
Common mistakes
- Turning the temperature up when it runs cool — The unit produces a fixed amount of heat. Turning it up slows the flow to reach the setting, which is exactly what makes it overheat and cut out.
- Opening the shower casing to look inside — There is a 40-amp supply behind it in a wet room. It is notifiable electrical work in a special location, and there is nothing user-serviceable in there anyway.
If it doesn't work
Hot for a minute, then cold, then hot again
Cause: Thermal cut-out cycling on restricted flow — Fix: Descale the head and clean the inlet filter.
Water flow visibly weaker than it used to be
Cause: Scale in head, hose or filter — Fix: Work through all three in that order.
No lights, no water, nothing
Cause: Isolator off, tripped breaker or unit failure — Fix: Check the pull cord and consumer unit; beyond that it is an electrician.
Trips the breaker when switched on
Cause: Element or wiring fault — Fix: Leave it isolated and call an electrician. Do not keep resetting it.
Questions people ask
Why is my electric shower worse in winter?
The incoming mains water is colder, so the same element has to raise it further. Many units have a summer and winter setting for exactly this; the winter setting cuts the flow rate to keep the temperature up.
Can I replace an electric shower myself?
No. Swapping the unit is fixed electrical work in a bathroom — notifiable under Part P in England and Wales, and controlled under the equivalent rules in Scotland and Northern Ireland — and the cable size and circuit protection have to suit the new unit's rating. It needs an electrician.
Does an electric shower need the stopcock fully open?
Yes. They are sensitive to supply pressure and flow, so a partly closed stopcock or isolating valve will cause exactly the overheating pattern people blame on the shower.