No Hot Water Coming Out of the Taps

Is the hot tap running cold, or not running at all?

People say "no hot water" for two quite different problems, and the fixes do not overlap. Before anything else, open a hot tap fully for a minute and a cold tap next to it.

Plenty of water from the hot tap, but cold: the water is getting through and is just not being heated. That is a boiler, cylinder or immersion problem, covered in why have I got no hot water.

A trickle, spluttering or nothing from the hot tap while the cold runs normally: the hot supply is starved or blocked. That is the problem this page deals with.

Nothing from the hot or cold taps: the whole supply is off. Check whether neighbours are affected and look at no water in the house instead.

One hot tap dead but others fine: the fault is local to that tap. The small isolating valve on the pipe under the basin may have been turned (the slot should run along the pipe, not across it), or the tap cartridge or aerator is blocked with scale.

Which hot water system do you have?

Where the hot water comes from decides where it can get stuck. Most London homes have one of three set-ups.

• Combi boiler, no tank anywhere: hot water is mains water heated on its way through the boiler. If the mains is weak, the hot is weak too, and below a minimum flow the boiler will not fire at all.
• Vented cylinder with a cold water tank in the loft: the loft tank feeds the cylinder by gravity. Hot taps usually run gently and depend entirely on that tank staying full.
• Unvented cylinder, usually a white or grey drum surrounded by valves, with a small safety pipe to a tundish: mains water feeds it through an inlet control group with a strainer and a pressure reducing valve. Hot taps run at mains pressure, limited by the pressure reducing valve.

Vented cylinder: empty loft tank or an airlock

With a loft tank, the most common reason for hot taps running dry is that the tank itself is empty. The float valve (the ballcock) that refills it has stuck shut or clogged with scale, or the mains pipe to it has frozen in a cold loft. The cylinder stays full, because the hot draw-off comes from the top, but nothing pushes water up and out to your taps. Our guide to the loft tank ballcock shows how to free a stuck float.

If the loft tank is full but the hot taps splutter and stop, air is trapped in the pipework, usually after the tank ran low or someone drained down. A common fix on a kitchen mixer tap, where the hot comes from the tank and the cold from the mains, is to open both taps and briefly block the spout so mains pressure pushes back up the hot pipe and moves the air. More methods are in airlock in pipes.

While the hot supply is starved, the cylinder normally stays full, so an immersion heater left on is not usually at risk. Switching it off until the tank refills costs nothing and removes any doubt, and never switch on an immersion in a cylinder that has been drained.

Take a torch into the loft and step only on joists or boarding. If the tank is overflowing instead of empty, the float valve is stuck open and needs attention soon.

Combi or unvented cylinder: the mains is not getting through

On mains-fed systems, a starved hot tap nearly always traces back to the cold supply into the boiler or cylinder. Start with the stopcock: it should be fully open, and a stopcock that was recently turned may be only partly open. Then check the kitchen cold tap. If mains flow is poor everywhere, the problem is the supply, not the hot water system, and low water pressure repair covers that.

If the cold is strong and only the hot is weak or dead, the restriction sits between the incoming main and the hot outlets. On a combi it is often the inlet filter, a small mesh inside the cold connection that clogs with grit after mains work in the street; on Worcester combis with no hot water it sits just ahead of the flow turbine. On an unvented cylinder it is usually the strainer in the inlet control group or a pressure reducing valve that has failed partly shut, which our guide to pressure reducing valve problems explains.

Unvented cylinders are covered by Part G3 of the Building Regulations, and their valves and safety devices should be left to an engineer who holds an unvented qualification. If water is running continuously into the tundish, or the cylinder is making loud noises, turn off the heating source and call for help.

Frozen pipes in a cold snap

If the hot taps stop during a hard frost, look for a frozen pipe before anything else. On gravity systems the pipes in the loft are most exposed, including the mains feed to the tank. On combis the cold feed can freeze where it passes an outside wall or runs through an unheated garage, and the boiler condensate pipe outside may freeze and lock the boiler out too.

Thaw frozen pipes slowly with warm cloths or a hairdryer on a low setting, starting from the tap end. Never use a blowtorch or boiling water, and have the stopcock ready in case the pipe has split. Our page on frozen pipes has the full routine.

When to call and what the engineer does

Call an engineer when the loft tank refills but the taps still run dry, when an unvented cylinder is involved at all beyond the stopcock, when you suspect a frozen pipe has split, or when the household cannot manage without hot water tonight.

The engineer checks the incoming mains flow and pressure, works along the supply from the stopcock to the hot outlets, and clears or replaces whatever is restricting it: a float valve, an inlet filter, a strainer, a pressure reducing valve or a frozen section of pipe. Our no hot water repair visit starts with the £60 call-out at any hour, and the repair price is agreed with you on site before any work starts.