No water coming out of the hot tap: causes and checks

One tap, or every hot tap?

Start by trying every hot tap in the property, including the bath and shower. The answer narrows things down more than anything else.

If only one hot tap has stopped, look under the basin or sink for a small isolation valve on the hot pipe. It has a slot you turn with a screwdriver: in line with the pipe is open, across it is closed. If it is open, the tap's cartridge or washer may have failed, or its aerator may be blocked with scale. Our guide to a tap cartridge or new tap covers those repairs.

If every hot tap has stopped, the problem is on the hot supply itself, and what you check depends on how your hot water is made.

If you have a combi boiler

A combi takes water straight from the mains, heats it as it passes through, and sends it to the hot taps. If cold taps are running at good pressure, the mains is fine, so the water is being stopped at or after the boiler.

Look underneath the boiler for the cold water inlet valve. After a service, a repair or other work nearby, it is sometimes left closed or only part open. It is normally a small valve with a slot or lever: in line with the pipe is open. If it was closed, open it slowly and try the hot tap.

In freezing weather, check whether any hot pipes run through an unheated space or an outside wall. A frozen hot pipe stops flow completely. Our guide to frozen water pipes explains how to thaw them safely. Some combis also have a small filter on the cold inlet, and all of them have a plate heat exchanger that can scale up in hard-water areas, which most of London is. A slowly reducing hot flow over weeks, ending in a trickle, points that way. Both need an engineer, because they are inside the boiler.

If hot water runs but stays cold, that is a different fault. No hot water but heating works covers a combi that is not heating the water.

If you have a cylinder and a tank in the loft

In a vented system, the hot water cylinder is filled from a cold water storage tank in the loft, not from the mains. If that tank empties, the hot taps slow and stop, while a kitchen cold tap fed from the mains keeps working normally. Upstairs cold taps and the toilet cistern may be affected too.

Check the loft tank. If it is empty or very low, the float valve that refills it has usually stuck, or the pipe feeding it has frozen or been turned off. Freeing a stuck float valve is sometimes enough to get it refilling, but a worn one needs replacing.

Once the tank refills, the hot taps may still splutter or stay dry because air has got into the pipework. That is an airlock. Our guide to an airlock in water pipes explains the safe ways to clear it. Also check that the valve on the cold feed pipe from the tank to the cylinder is open; they are occasionally closed during other work and forgotten.

If you have an unvented cylinder

An unvented cylinder, such as a Megaflo, is fed directly from the mains through a group of valves near the cylinder: an isolation valve, a strainer, a pressure reducing valve and safety valves. If the cold taps elsewhere are fine but no hot water comes out, the flow into the cylinder is usually being stopped by that valve group.

The one thing to check yourself is that the main isolation valve on the cold inlet to the cylinder is fully open. Beyond that, a blocked strainer or a failed pressure reducing valve needs a qualified engineer. Our guide to a cylinder pressure reducing valve fault describes the symptoms.

Do not open, adjust or remove any of the safety valves or the valve group yourself. Unvented cylinders store hot water under pressure and the work must be done by someone qualified to work on them.

If the cylinder is making loud noises, the tundish is discharging very hot water or steam, or the pipework around the cylinder is extremely hot, switch off the boiler and immersion heater and call for help straight away.

When the whole house has no water

If the cold taps are also dry or weak, the problem is the mains supply, not your hot water. Check with neighbours and your water supplier, and look at your stop tap. Our guide to no water coming out of the taps explains what to check in that case, including a burst or supply fault in the street.

What an engineer will check

If the simple checks do not bring the hot water back, an engineer will work along the hot supply from its source. Depending on the system, that means checking the valves and filters on the boiler's cold inlet, the flow sensor and plate heat exchanger on a combi, the float valve, tank feed and cylinder feed on a vented system, or the strainer, pressure reducing valve and inlet pressure on an unvented cylinder. On a single tap, the cartridge and the isolation valve are replaced or cleared.

It helps to tell us which taps are affected, what kind of system you have, whether anything was worked on recently and whether the weather has been freezing.

Getting your hot water flowing again

Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road, and works on combis, vented cylinders and unvented cylinders. Gas work on the boiler is carried out by Gas Safe registered engineers. Call 020 4652 8585 and describe what you have checked.

Our call-out charge is £60, and the engineer explains what they have found and what the repair involves before starting any work. You can read more on our hot water repair page and, for unvented systems, our unvented cylinder servicing page.