No Water Coming Out of the Hot Tap? Causes and Fixes

Updated July 2026 · Emergency Plumber Chelsea

Start by working out which system you have, because the causes are different. If there is a large cold water tank in the loft and a copper hot water cylinder in an airing cupboard, you have a gravity-fed or vented system, and the hot water relies on the tank to push it through the pipes. If there is no tank and the boiler heats water on demand, you have a combi. If there is a cylinder but no loft tank, and the cylinder has a pressure gauge and a set of valves on the pipe going into it, it is an unvented cylinder running at mains pressure. Our guide to mains pressure and gravity-fed plumbing explains the difference in more detail.

Then check whether it is every hot tap or just one. Try the kitchen, the bathroom basin and the bath. If one hot tap is dry but the others flow, the fault is local: a small isolation valve under the basin that has been turned off, a blocked aerator on the spout, or a worn cartridge in a mixer tap. Unscrew the aerator and rinse it, and check the slotted valve on the hot pipe under the basin is turned so the slot runs along the pipe. If the tap still will not run, the cartridge or valve inside it has likely failed and needs replacing.

On a gravity-fed system, if no hot tap runs at all, look in the loft tank first. A float valve that has stuck shut, a supply pipe that has frozen, or a valve that someone turned off during work can leave the tank empty or very low. The cylinder is fed from that tank, so when it empties, the hot taps stop. Cold taps upstairs that come off the same tank may also slow down, while the kitchen cold tap, which comes straight off the mains, keeps running. Our guide to cold water storage tank problems covers how to free a stuck float valve. Once the tank refills, the hot taps usually come back, although you may need to clear an airlock.

Airlocks are the next most common cause, especially after the water has been off, the tank has run dry or someone has drained part of the system. A bubble of trapped air sits at a high point in the pipe and the low pressure of a gravity system is not enough to push it through. The tap may splutter, hiss or give nothing at all. The usual fix is to connect the hot tap to a mains-fed cold tap with a hose and use the mains pressure to push the air out, which our guide on how to clear an airlock in pipes explains step by step.

In cold weather, suspect a frozen pipe. Hot water pipes can freeze as easily as cold ones when they run through an unheated loft, an outside wall, a cold basement or under a suspended floor, and the feed pipe from the loft tank to the cylinder is a common victim. If the problem appeared on a frosty morning, look for pipes in cold spaces and warm them slowly with a hot water bottle, a towel soaked in warm water or a hairdryer on a low setting. Never use a blowtorch or naked flame. Check carefully for splits as the pipe thaws, and keep the stopcock handy in case it has burst. Our guide on how to stop pipes freezing covers lagging and prevention.

On a combi boiler, no flow from the hot taps with good cold flow points in a different direction. Check the isolation valve on the cold water inlet underneath the boiler is fully open, because it is sometimes closed during other work and forgotten. Many combis also have a small filter on that inlet which collects debris and limescale, and in hard-water London it can block enough to choke the hot supply. A blocked plate heat exchanger or a faulty diverter valve can also restrict flow. These are jobs for a Gas Safe engineer, as they mean opening the boiler, but it is worth checking the display for a fault code and noting it before you call.

With an unvented cylinder, the incoming mains passes through a pressure reducing valve and usually a line strainer before it reaches the cylinder. If the strainer blocks with debris, or the pressure reducing valve fails, the hot taps can drop to a trickle while the cold taps, often fed before that valve, stay strong. Servicing the strainer and valves is part of the annual check an unvented cylinder needs, and it should be done by someone qualified to work on unvented systems. Our guide to unvented and vented hot water cylinders explains how these systems work.

It is also worth separating no flow from no heat. If water comes out of the hot tap but it is cold, that is a heating problem, not a supply problem, and our guides to no hot water and an immersion heater not working are the better place to start. Mixing the two up is common and it sends people looking in the wrong place.

Chelsea's housing adds a few twists. Mansion blocks often have communal tanks or boosted supplies, so a problem affecting several flats at once may sit with the building rather than your flat, and the porter or managing agent should be told. Period houses frequently have long, awkward pipe runs from a loft tank down several floors, which makes airlocks more likely after any drain-down. Basement conversions sometimes have hot water pipes running through unheated vaults that freeze in a cold snap. If no tap in the flat is running at all, hot or cold, our guide to no water in the house covers the supply checks.

If the hot taps are still dry after these checks, or you suspect a frozen or split pipe, a blocked combi filter or a failed valve, call Emergency Plumber Chelsea on 020 3002 6667. We deal with airlocks, tanks, cylinders and combi faults through our plumbing repairs service and boiler repair service across SW3, SW10, Knightsbridge, Sloane Square, South Kensington and Fulham. There is no call-out fee on jobs over 3 hours.

Quick tips

• Check every hot tap: if only one is dry, look at that tap's isolation valve, aerator and cartridge first.
• On a gravity system, look in the loft tank; if it is empty, the hot taps stop even though the kitchen cold tap works.
• After the water has been off, clear an airlock by linking the hot tap to a mains cold tap with a hose.
• In frosty weather, thaw frozen pipes slowly with warmth, never a naked flame, and watch for splits.
• On a combi, make sure the cold inlet valve under the boiler is fully open before calling.

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