Hot Water Tap Not Working? Why One Tap Has No Hot Water
When the hot water works everywhere except one tap, the boiler is rarely the problem. It's usually a closed isolation valve, a failed cartridge, a blocked aerator, a mixing valve or an airlock on that one outlet. How to find which, and when to call a plumber.
If the hot tap isn't working on one fitting but the other hot taps in the house run hot, the fault is almost always on that tap or the pipe feeding it, not the boiler. Check in this order: the isolation valve on the hot pipe under the tap may be closed or partly closed; the aerator on the spout may be blocked with scale, which on a combi can cut the flow too low for the boiler to fire; the tap's cartridge or headgear may have failed; a thermostatic mixing valve under the basin or bath may have stuck; or, after plumbing work on a tank-fed system, an airlock may be stopping the flow. If no hot tap in the house works, the fault is with the boiler, cylinder or controls instead.
Key Takeaways
- One tap with no hot water, others fine: the fault is at that tap or its pipe, not the boiler.
- Check the isolation valve under the tap first. The slot should run along the pipe.
- A scaled aerator can reduce flow so much that a combi boiler doesn't fire for that tap.
- Single-lever mixers with no hot water often need a new cartridge.
- No hot water at any tap is a boiler, cylinder or controls fault, not a tap fault.
If the hot tap isn't working on one fitting but the other hot taps in the house run hot, the fault is almost always on that tap or the pipe feeding it, not the boiler. The usual causes are an isolation valve on the hot pipe that has been closed or knocked, an aerator blocked with scale, a failed cartridge or headgear, a stuck thermostatic mixing valve, or an airlock after plumbing work. Most of these can be checked in a few minutes with a screwdriver and a bowl. This guide goes through them in order, and explains what's different if you have a combi boiler or a hot water tank.
One tap or every tap?
Before anything else, run the hot tap on every basin, bath, shower and sink in the house for a minute or so.
- Only one tap has no hot water. The boiler or cylinder is working. The fault is at that tap, its valve or its pipe. Carry on with this guide.
- All hot taps run cold. The problem is the boiler, cylinder, immersion heater or controls. See our guides to no hot water but the heating works and our no hot water service.
- The tap runs hot, but not hot enough. That's usually a mixing valve or boiler setting. See our guide to hot water not hot enough.
- Hot water comes out of the cold tap. That's a different fault, covered in hot water coming out of the cold tap.
Why one hot tap stops working
| What you notice | Most likely cause |
|---|---|
| Nothing comes out of the hot side at all | Closed isolation valve, failed headgear or cartridge, or an airlock |
| Hot side runs, but only cold water and a weak flow | Blocked aerator or restricted valve (especially on a combi) |
| Single-lever mixer only gives cold whichever way you turn it | Worn or scaled cartridge |
| Basin or bath runs cold, other outlets fine, newer home | Thermostatic mixing valve stuck or blocked |
| Started straight after plumbing or kitchen work | Valve left closed, airlock or pipes swapped |
| Started in a cold snap, tap on an outside wall | Frozen pipe |
The isolation valve. Most taps have a small valve on each supply pipe underneath, with a screwdriver slot. The Water Fittings Regulations describe these as servicing valves, fitted so a single fitting can be shut off for maintenance. When the slot runs along the pipe the valve is open; when it's across the pipe it's closed. They get turned off during other jobs and knocked when cupboards are packed, and a half-closed valve can cut the flow to a trickle.
The cartridge or headgear. Mixer taps use ceramic cartridges, and older taps use headgear with a washer. Scale or wear can stop the hot side opening, or a broken part inside can leave the handle turning with nothing happening. On a single-lever mixer, a cartridge that only gives cold whichever way you move the lever usually needs replacing. Our guide to a tap that won't turn off explains how cartridges and headgear work.
A thermostatic mixing valve. Many newer bathrooms have a small valve under the bath or basin that blends hot and cold to a safe temperature. Approved Document G requires the hot water to a bath in a new home to be limited to 48°C, which is usually done with one of these. If its internal parts scale up or stick, the outlet can run cold while every other tap is hot. They need servicing or replacing rather than adjusting blind.
Combi boilers and low flow
A combi boiler heats water only when it senses water flowing through it. If the flow is too low, the boiler doesn't fire and the tap runs cold. That's why a single tap with a badly scaled aerator, a half-closed valve or a restricted cartridge can give only cold water on a combi, while taps with a good flow are hot.
The quick test is to unscrew the aerator (the mesh at the end of the spout) and run the hot tap without it. If the water gets hot, clean or replace the aerator. Soaking it in descaler or white vinegar usually clears it. If the whole house has weak hot flow, see our guide to low water pressure.
Tank-fed systems and airlocks
If your hot water comes from a cylinder fed by a tank in the loft, the hot taps rely on gravity. After the system has been drained, for a new tap or a leak repair, air can get trapped in a high point of the pipe and stop the hot water reaching one tap. The tap may splutter, run briefly then stop, or give nothing. Our guide to an airlock in water pipes explains the safe ways to clear one.
If the cold tank in the loft is low or empty, hot taps upstairs are often the first to fail. See cold water storage tank problems.
One tap with no hot water?
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What you can check yourself
- Check the isolation valve on the hot pipe under the tap. Turn the slot so it runs along the pipe. If it won't turn or feels gritty, don't force it.
- Clean the aerator. Unscrew it from the spout, run the tap without it for a moment, then soak it in descaler or vinegar.
- Run the hot tap for two or three minutes. On a long pipe run from the boiler or cylinder, it can take a while for hot water to arrive. That's slow, not broken.
- Check for a mixing valve under the bath panel or basin. If there is one and the outlet runs cold, it's likely the cause.
- Think about recent work. If a tap, sink or appliance was changed recently, ask whoever did it to check the valves and connections.
- In freezing weather, check whether the pipe to that tap runs along an outside wall or through a cold void. See our guide to frozen pipes.
When to call a plumber
Call a plumber if the valve and aerator are fine and the tap still gives no hot water, if the cartridge or headgear needs replacing and you can't identify the part, if a mixing valve is involved, if you suspect an airlock you can't clear, or if the tap stopped working after other work and you're not sure what was changed. If no hot tap in the house works, it's a boiler or cylinder fault and needs a Gas Safe registered engineer for a gas boiler.
We charge £95 an hour for labour, plus a £60 call-out that's waived when the job runs over 2 hours. Parts are extra and we confirm the price before any work starts. Our tap repair, kitchen tap repair and hot water pressure services cover homes and flats across London, and the pricing page explains how jobs are charged.
Frequently Asked Questions
Why is there no hot water from one tap only?
Because the fault is local to that tap. The most common causes are a closed or partly closed isolation valve on the hot pipe, a blocked aerator, a failed cartridge or headgear, a stuck thermostatic mixing valve, or an airlock in the pipe after plumbing work. If every other hot tap runs hot, the boiler or cylinder is working.
Why does my kitchen tap have no hot water but the bathroom does?
Check the isolation valve on the hot pipe under the sink, as it's often knocked or closed during other work, then unscrew and clean the aerator on the spout. On a single-lever mixer, a worn cartridge can stop the hot side opening. On a combi boiler, a scaled aerator or restricted valve can cut the flow below what the boiler needs to fire, so the tap runs cold.
Can a blocked aerator stop hot water coming through?
It can reduce the flow a lot, and on a combi boiler that matters. A combi only fires when it detects enough flow, so a tap with a badly scaled aerator may run cold while other hot taps work. Unscrewing the aerator and soaking it in descaler or vinegar often restores both the flow and the hot water.
Why does my hot tap run cold after plumbing work?
On a tank-fed system, draining the pipes can leave an airlock that blocks the hot supply to one tap. On any system, an isolation valve may have been left closed, or the hot and cold pipes may have been reconnected the wrong way round. Check the valves first, then ask whoever did the work to come back and check the connections.
Do I need a plumber or a gas engineer if one hot tap isn't working?
A plumber, in most cases. If other hot taps work, the boiler is doing its job and the fault is in the tap, valve or pipe, which is plumbing work. You only need a Gas Safe registered engineer if the boiler itself turns out to be the problem, for example if no tap in the house gets hot water.
Sources and further reading
Source links checked 28 September 2026. Scheme rules and manufacturer instructions can change; use the current official guidance for your account or exact appliance.