No hot water? What to check in the first ten minutes

The first question splits the whole problem in two

Turn a radiator on. Not because you want heat — because the answer tells you where to look.

• No hot water, but the heating works. The boiler is firing. Something between the boiler and your taps has failed: on a combi, usually the diverter valve; on a system or gravity setup, the cylinder, its thermostat, or the motorised valve that sends hot water to it.
• No hot water and no heating. The boiler is not firing at all, or is not being asked to. Power, controls, pressure, gas, or a frozen condensate pipe in a cold snap.

Say which of these it is when you call. It is the single most useful sentence you can give an engineer, and it changes what goes on the van.

The five checks, cheapest first

1. Has anything tripped?

Look at the boiler. Any display, any backlight, any standby light at all? If it is completely dead, it is an electrical supply problem, not a boiler problem.

Go to the consumer unit and look for a switch sitting in the down position or halfway. The boiler may have its own breaker, or it may share one with the sockets on that floor — which is why a boiler can die the moment a kettle or a shower pump gives up somewhere else in the house. Also find the fused spur: usually a switched socket-style plate near the boiler, on an airing cupboard wall, or above a worktop. It has a 3A fuse in it, and that fuse blows.

If a breaker trips again as soon as you reset it, stop. Something is faulting and that is an electrician's job, not a plumber's.

2. Is the programmer actually calling for hot water?

This one embarrasses people, which is exactly why it is worth checking before you pay someone to check it for you. Programmers get nudged, lose their settings after a power cut, sit in a holiday or away mode nobody set on purpose, or run on a clock that never went forward in March.

Put the hot water to constant or on, not timed, and wait. Then check the cylinder thermostat if you have one — a dial strapped to the side of the cylinder under the insulation jacket, often set somewhere around 60°C. If it has been wound down, nothing will call for heat.

On a combi there is no cylinder and no schedule for hot water at all. Hot water is on demand, all the time. If yours appears to be on a timer, you have a system boiler and a cylinder somewhere, even if you have never found it.

3. Is the hot water temperature dial where you think it is?

Most boilers have two controls, one for heating and one for hot water, and they look alike. Manufacturers point out that water set below about 30°C feels cold at the tap even though the boiler is working perfectly. A dial knocked while cleaning produces exactly the symptom you are describing. Turn it up, run a tap for a full minute, and see.

4. What does the pressure gauge say?

On a sealed system — a combi or a system boiler — there is a gauge on the front of the boiler or on the filling loop below it. Cold, it should read roughly 1.0 to 1.5 bar. Below about 0.5 bar most boilers lock out and refuse to fire, which takes your heating and your hot water with it.

If it reads zero or near it, that is a real finding. Note the number before you touch anything. It is the most diagnostically useful thing in the house and most people top it up and forget it, which destroys the evidence.

You can repressurise it yourself. What matters more is how often you have had to. A sealed system is closed and should not lose water. Twice a year is nothing. Monthly is a weeping joint or a failed expansion vessel. Weekly is an active leak, and that one is ours — see a boiler that keeps losing pressure for what the frequency tells you.

5. Is there water anywhere it should not be?

Two minutes with a torch, and this is the check that decides whether you need a heating engineer or us.

• Under and behind the boiler casing — you are looking for staining or a damp patch on the floor, not opening anything.
• The discharge pipe outside, the small pipe from the boiler or the cylinder that ends above a drain. A drip whenever the system fires means a valve or a vessel has failed. Water pouring from an unvented cylinder's discharge is not a plumbing nuisance, it is a safety device doing its job.
• The base of the cylinder and the pipework at its top, including the airing cupboard floor.
• Any ceiling below the boiler or the cylinder, and any warm or damp patch underfoot that has no reason to be there.

Found water? Say so immediately when you call. A boiler that is leaking and a boiler that has simply stopped are different jobs with different people attending.

Reading the pattern

What you have	Most likely	Free to fix?
Heating fine, taps cold, combi	Diverter valve stuck	No — parts and labour
Heating fine, taps cold, cylinder in the house	Cylinder thermostat, motorised valve, or the programme	Sometimes — check the programme first
Both dead, boiler display blank	Tripped breaker or blown fused spur	Often yes
Both dead, gauge near zero	Low-pressure lockout — and something is losing water	Top-up is free; the leak is not
Both dead after a hard frost, boiler gurgles then stops	Frozen condensate pipe outside	Often yes — warm water on the pipe, never boiling
Hot for thirty seconds then cold	Cylinder emptied and reheating, or a failing diverter	No
Gauge drops week after week	An actual leak, usually hidden	No — this is the detection job

What you should not touch

There is a short list, and it is short for good reasons.

• Anything behind the boiler casing. Gas appliance work is restricted to Gas Safe registered engineers under the Gas Safety (Installation and Use) Regulations 1998. Removing a cover to look is not a grey area you want to be in.
• Anything on an unvented cylinder. An unvented cylinder holds a large volume of very hot water at mains pressure, which is why its installation and servicing sit under the Building Regulations and require someone holding the unvented qualification. Its valves and expansion vessel are theirs to touch, and capping or plugging a running discharge pipe removes the only safe route for that stored energy.
• A breaker that trips repeatedly. Reset once. If it goes again, leave it off.
• Immersion heaters on a timer you do not understand. An immersion is a useful backup while you wait, but leaving one on constantly on a cylinder with a failed thermostat is how people end up with a scalding tap.

Yes, a good firm wants you to have checked

Be blunt about this, because it is where the money is. Some of the calls that come in as an emergency are a programmer in away mode, a 3A fuse, or a dial someone turned down. If you check those five things before you phone, one of three outcomes follows, and all of them are better for you:

1. You fix it yourself for nothing and do not need us at all.
2. You find something specific — gauge at zero, discharge dripping, damp under the boiler — and whoever attends arrives knowing what the job is.
3. You have ruled out the cheap causes, so the visit starts at the real fault instead of spending the first twenty minutes doing what you could have done.

Any competent engineer will be glad of that. If a firm bristles at being told what you already checked, or insists on re-running the free checks on the clock before discussing anything else, that tells you something about how they bill. The five-minute fix that stays a five-minute fix is not a loss to us; it is the cheapest possible version of a good outcome, and it is how people decide who to call next time.

When it becomes a leak job

Most no-hot-water calls are not leaks, and we will say so. Diverter valves, thermostats, ignition faults and gas supply problems are for a heating engineer, and pretending otherwise would waste your money.

It is ours when water is going somewhere it should not. A pressure gauge that will not hold, a system needing topping up weekly, an unexplained warm patch on a floor, a stain on a ceiling under the airing cupboard — that is a hidden loss, and finding it is a different discipline from fixing a boiler. The circuit is isolated and pressure-tested to confirm the loss is real and size it, then traced with thermal imaging and, on a drained circuit, tracer gas, so one board comes up rather than a whole floor. That work sits under boiler and heating leak repair, and our own handymen close the opening back up afterwards.

What it costs

£150 per hour, agreed before we attend, and no call-out fee. If we are looking for a hidden leak and do not find it, you do not pay for the time we spent looking. Detection visits come with a written report prepared to support a trace-and-access claim, though what the policy pays is the insurer's decision. Full rates are on the pricing page.

If the kitchen tap runs hot and it is only the shower that has gone cold, the checks are different, and no hot water in the shower goes through them.