No Water Coming Out of the Hot Tap? Why, and What to Do

First, three quick checks

These take two minutes and tell you where to look next.

• Is it every hot tap, or just one? One dry tap points to that tap or the small valve under it. Every hot tap dry points to the supply to the cylinder or boiler.
• Do the cold taps work? If the kitchen cold is dead too, it is the mains: a supply problem in the street or a closed stopcock. Check your water company's website for works in your area.
• Which system do you have? A tank in the loft means tank fed. Brass valves and an expansion vessel beside the cylinder mean unvented. No cylinder at all, just a boiler on the wall, means a combi.

Tank fed cylinder: check the loft tank first

On a tank fed system, the hot water is pushed out of the cylinder by water from the cold water storage tank in the loft. If that tank is empty, nothing comes out of the hot taps even though the kitchen cold, which comes straight off the mains, works normally. The bathroom cold taps and the toilet cistern are often fed from the same tank, so if they are slow or dry too, the tank is the prime suspect.

Look in the tank. If it is empty or low, the ball valve that refills it has stuck, its washer has failed, or the mains pipe feeding it has frozen or been turned off. Pressing the float arm down gently should let water in. If water rushes in, the valve had stuck and may stick again, so it is worth replacing. If nothing comes, the supply to the tank is the problem.

Once the tank refills, the hot taps may spit and splutter before they run properly. That is air working its way out. If they stay dry or keep spitting, you may have an airlock, and our guide to an airlock in hot water pipes explains how to clear one.

Tank fed cylinder: a closed valve on the cold feed

The pipe from the loft tank into the bottom of the cylinder usually has a gate valve on it, in the airing cupboard. If someone has closed it, for a repair, a drain down or by accident while reaching for something else, the cylinder stays full but no water can flow out of the hot taps. Turn it anticlockwise to open it. If it spins without opening, the gate inside has broken and the valve needs replacing.

In cold weather: a frozen pipe

From the first hard frost of the autumn, a frozen pipe becomes the most likely cause of a sudden dry hot tap on a tank fed system. Pipes in the loft, in outside walls, under suspended floors and in unheated extensions are the ones that freeze. The cold feed from the loft tank to the cylinder, and the mains pipe that fills the tank, are both at risk.

If you can find the frozen section, it is often colder to the touch, sometimes with frost on it. Warm it gently with a hairdryer on a low setting, a hot water bottle or warm cloths, working from the tap end back towards the freeze, with the tap open so water can escape as it thaws. Never use a blowtorch or naked flame.

Watch the pipe as it thaws. Ice expands, and a pipe that has frozen can split, so it may start leaking once the water flows again. Know where your stopcock is before you start, and our guide, where is my stopcock, helps if you do not. If a pipe has split, turn off the water and see our burst pipe repair service.

Unvented cylinder: the inlet group

An unvented cylinder runs off the mains, so if the cold works but the hot is dead, the problem is almost always on the cold inlet to the cylinder. The usual causes are:

• The isolating valve on the incoming mains pipe has been closed, often after a repair or a service.
• The inlet strainer, a fine mesh filter in the brass valve set, has blocked with debris, typically after mains works in the street stirred up sediment.
• The pressure reducing valve has failed closed. Our guide to the pressure reducing valve explains what it does and how it fails.

Unvented cylinder: what is safe to check yourself

Check the isolating valve before the brass valve set is open. A lever or slot along the line of the pipe means open. Beyond that, the strainer and the pressure reducing valve are inside the cylinder's safety set, and cleaning or replacing them means isolating and depressurising a hot, sealed cylinder. That is work for an engineer with the G3 unvented qualification, and our unvented cylinder repair service covers it. If the hot water has gone weak rather than stopped completely, our guide to low hot water pressure covers the same parts in more detail.

Combi boiler: no hot water flow at all

A combi heats mains water as it passes through, so a hot tap with no flow at all, while the cold runs normally, means the water is not reaching or leaving the boiler. Check the valve on the cold mains pipe under the boiler is open. Beyond that, many combis have a small filter on the cold inlet that can block with debris, and a heavily scaled heat exchanger can choke the flow. Both are jobs for a Gas Safe engineer.

If water flows but it is cold, that is a different fault, and our page on no hot water from a combi boiler covers it.

Only one hot tap is dry

If every other hot tap works, the fault is local to that tap. Look under the basin or sink for a small isolating valve on the hot pipe, usually with a screwdriver slot. It may have been turned off. If it is open, the tap cartridge or washer may have failed, or the aerator on the spout may be blocked with scale, which is common with London's hard water. Unscrewing the aerator and rinsing it is a two minute job. A failed cartridge needs replacing.

Switch the heat off while you sort it out

While no water is flowing, turn off the immersion heater at its wall switch and set the boiler hot water to off. A tank fed cylinder with an empty loft tank can partly drain, leaving the immersion element running out of water, which burns it out. And there is no point paying to heat water you cannot use. Our guide on how to turn off hot water supply from a cylinder explains the heat side and the valves in order.

When to call us

Call us on 020 4652 5111 or send an enquiry if the loft tank will not refill, a valve will not open, a pipe has split, or you have an unvented cylinder and the isolating valve is already open. A photo of the cylinder and the valves on its cold pipe tells us a lot before we arrive. We have 20 engineers across London, and our rate is on the pricing page, agreed before anyone attends.