No hot water? Start with what you can see
Work out which of these is happening and you have usually narrowed a hot water fault to one component before anyone attends.
Almost every hot water failure falls into one of four groups, and they have different causes. Nothing hot anywhere usually means the heat source has stopped or the controls have. Heating works but the taps are cold points at whatever splits the two: a diverter valve on a combi, a motorised valve or the cylinder coil on a stored system. Hot water that is lukewarm, or hot then cold, is nearly always a thermostat, a scaled heat exchanger or a cylinder that has lost its stratification. Water escaping anywhere near the cylinder is a different problem entirely and the only one on this list that is urgent.
A handful of these you can resolve yourself in five minutes and we will say so on the page rather than sell you a visit. A programmer knocked onto an off schedule, a boiler that has locked out and needs one reset, an immersion switched off at the wall: all common, all free to fix. What matters is knowing where that line sits, because past it you are into sealed systems holding mains pressure, and an unvented cylinder is not something to experiment on.
If water is actively escaping, stop reading and turn the stopcock off. Everything else can wait for a diagnosis.
Hot water cylinder leaking, overheating or making noise
Where a hot water cylinder actually leaks from, and why a puddle at the base rarely means the tank has failed. Trace it to a fitting before you replace it.
Read thisHot water cylinder making noise: what each sound means
Kettling, banging, hissing or humming from a hot water cylinder. What each noise means, which are scale, which are water hammer and which are urgent.
Read thisHot water scalding hot and the cylinder overheating
Hot water gone scalding? What to switch off first, how to tell an overheating cylinder from a failed blending valve, and when it is urgent.
Read thisHot Water Tank Not Heating: How to Find the Fault
A hot water tank that will not heat is the immersion, the boiler coil, a stuck valve or a tired thermostat. Work out which in ten minutes, before you call.
Read thisHow Long Does Hot Water Take to Heat Up?
A 3kW immersion needs roughly 2 to 3 hours for a full cylinder. A boiler coil does it in under an hour. Real timings by tank size and heat source.
Read thisImmersion Heater Not Working
Immersion heater not working? Check the power, the switch, the timer, the thermostat, the cut-out and the element in that order, and know what is safe.
Read thisNo hot water but the heating works
Heating fine but no hot water? It is usually a combi diverter valve, a motorised valve, or a cylinder coil or stat. How to tell which one you have.
Read thisNo hot water from a combi boiler
Heating works but the taps run cold? The usual causes are the diverter valve, the flow sensor, a scaled plate heat exchanger or low flow at the tap.
Read thisNo hot water in the shower
Why a shower runs cold when the taps are hot: thermostatic cartridge, failed check valves, scale, electric shower element, or the cylinder itself.
Read thisPressure Relief Valve Leaking: What to Do and Why It Happens
Why a pressure relief valve leaks, how to tell a heat fault from a valve that will not seal, what to switch off first, and when it is urgent.
Read thisTundish Dripping: What the Water Is Telling You
Water in the tundish means a safety valve has opened. A drip and a steady flow mean different faults. How to read it, and why it must never be capped.
Read thisWater not getting hot
Why hot water runs lukewarm or never gets hot: combi flow rate, a scaled plate heat exchanger, a cylinder coil or stat, and what to check yourself first.
Read this
Which of the four groups you are in, and where to read next
The page that carries this whole section is no hot water but the heating works, because that is the shape the fault takes most often and because the chain it walks is the same chain every other page here narrows down. Radiators warm, taps cold, and somewhere between the heat source and the tap something has stopped handing the heat across. On a combi that is the diverter valve. On a stored system it is the motorised valve, the cylinder coil or the control that should have called for either. Read that first and the rest of this list becomes a question of which link you have landed on.
If the taps are cold and the radiators are cold with them, the heat source itself has stopped. On a combi the boiler is the water heater, so no hot water from a combi boiler is where that case belongs, and the display usually has something to say about it. On a stored system the boiler can be running perfectly while the hot water never arrives, which is why hot water tank not heating exists as a separate page: the fault is the cylinder or what feeds it, not the appliance. Immersion heater not working covers the backup element, and it is worth knowing about before you assume a locked out boiler means a cold bath, because a cylinder with a working immersion does not care what the boiler is doing.
Lukewarm, or hot then cold, is its own group and it is the one people live with longest. Water not getting hot is the page for it: a thermostat set or failed low, a plate heat exchanger silted up with scale, a cylinder that has lost the layering that keeps the hot at the top. No hot water in the shower is the narrower case where every other tap in the property is fine, which usually moves the fault to the mixer, the cartridge or the pressure feeding that one outlet rather than to the system. How long does hot water take to heat up is there for the reader who has no fault at all and is measuring a normal reheat against an expectation nobody ever set for them.
Water escaping near the cylinder is the urgent group and the only one on this hub that will not wait. Hot water cylinder leaking, overheating or making noise sorts the three symptoms that arrive together more often than they look like they should, because an overheating cylinder and a discharging cylinder are frequently the same fault seen from two ends. Tundish dripping and pressure relief valve leaking are the two discharge faults people most often decide to ignore, and both are the safety system reporting that something upstream of it has already failed. Hot water scalding hot and the cylinder overheating covers the temperature side of that, and hot water cylinder making noise takes each sound in turn, because kettling, banging and a steady hiss are three different problems with three different fixes.
Before any of it, no hot water checklist before you call is five minutes well spent. It is the list of things that cost nothing to put right, and we point people at it ahead of a visit deliberately. Where the answer is genuinely a repair on a sealed system, unvented cylinder repair is where these pages lead, because a cylinder holding mains pressure is the one part of this chain that is not something to work on yourself.
Not sure which of these it is? Tell us what the taps are doing.