01 Sept 2026
You turn the shower on, wait, and the water never gets warm. Before you assume the heater is finished, work through the checks below. Some cost nothing, and the ones that do not solve it still speed up the diagnosis, because you will be able to say exactly what the unit is doing.
First, know which type you have, because the checks differ.
Instant or storage?
An instant heater is the small box on the bathroom wall, usually with a temperature dial and a switch on it. It heats water as it flows through, so it never runs out, but it can only heat so much at a time.
A storage heater is a tank, normally in the ceiling space above the bathroom or out in the service yard, with a switch or isolator outside. It keeps a volume of water hot and ready, and once that volume is used it needs time to reheat.
If you are not sure which you have, the tank is the giveaway.
The checks worth doing first
- Is it switched on? Obvious, and still worth doing. Check the switch on the unit, the pull cord or wall switch outside the bathroom, and the isolator. A heater switched off and forgotten is a very ordinary cause of no hot water.
- Has the breaker tripped? Open the consumer box and look for a switch sitting out of line with the others. If you reset it and it holds, fine. If it trips again, leave it off and stop there. A heater that keeps tripping is not a glitch, it is the breaker doing exactly what it is there to do.
- Storage heater: has it had time? After a long shower, or several in a row, the tank has no hot water left in it and needs to reheat. If the second person always gets a cold shower and the first never does, that is capacity rather than a fault.
- Is the temperature turned down? Dials get nudged, especially on a unit within reach of children.
- Instant heater: is the flow too high? An instant heater goes lukewarm rather than cold when water runs through it faster than it can heat. Turn the flow down and see whether the temperature comes up. If it does, that is the unit working as designed.
- Is it one outlet, or all of them? If the basin runs hot and the shower does not, the heater is doing its job and the problem is at the shower mixer or diverter.
Things not to do
Do not keep resetting a breaker that trips again. Do not open the heater casing. Do not test wiring, and do not touch the unit while standing in water. If you can see water coming from the heater itself, switch it off at the isolator, close the inlet valve if you can reach it safely, and call.
What is usually wrong
If the checks above did not explain it, the faults we see most are a failed heating element, a thermostat that has stopped calling for heat, or, on a storage unit that has been in service a long time, sediment sitting in the tank. On instant units, a clogged inlet filter or a flow sensor that no longer registers the water going through are both common.
Age is a fair guide. Manufacturers generally expect a heater to last years rather than decades, so a unit that has been up there a very long time and has already been repaired once is telling you something.
Where the two trades divide, and why it matters
This part surprises people, so it is worth being plain.
We handle the plumbing side of a water heater: the unit itself, the mounting, the pipework, the valves, the isolation, and commissioning it once it runs. The electrical work is a different trade. Electrical connection and electrical fault-finding must be carried out by a Licensed Electrical Worker, which is a separate qualification from ours.
That is why a heater fault sometimes needs two people. It is not a way of passing you around. Where your job needs both, we coordinate so the visits line up rather than leaving you to chase it, and the electrical work is quoted separately.
Repair or replace
If water is coming from the tank body itself, that is not repairable. If a single part has failed on an otherwise sound unit, repair is the sensible choice. If it has been repaired before and is failing again, you are paying twice toward a replacement you will end up buying anyway.
Tell us the brand, the age and what it is doing, and we will tell you which of those three you are in. Our water heater repair page sets out what a diagnosis covers, and the pricing page shows where common jobs start. We supply heaters as well as fitting them, so you need not source a unit yourself.
When to call a plumber
Call once the switch, the breaker and the flow rate are ruled out and the water is still cold. Call straight away, whatever the checks say, if the unit is leaking, tripping repeatedly, making unusual noises or smelling of burning, and leave it switched off until someone has looked at it.