Step 1: Identify your system type
First, work out what kind of system you have. A combi boiler heats water as you use it and has no tank. A system or conventional boiler heats a stored cylinder, which is usually in an airing cupboard.
An electric immersion heater is a separate heater inside a cylinder. Knowing your type matters, because each fails in a different way. Look at your boiler label or manual if you are unsure.
Combi boiler: no hot water
Check the boiler display for a fault code, and look at the pressure gauge. Low pressure can stop the boiler heating water. Top it up if your manual says how, since many boilers have a filling loop.
If the heating works but the hot water does not, a part may be faulty. A diverter valve is one example. Because the fault is inside the boiler, call a Gas Safe registered engineer.
System boiler with cylinder: no hot water
Check the programmer and cylinder thermostat. They may be off or set too low. Make sure the boiler is on and the timer calls for hot water.
If the boiler runs but the cylinder stays cold, a motorised valve may have stuck. This is a job for a heating engineer, while a simple reset may help in some cases.
Conventional boiler with vented cylinder: no hot water
These systems use a cold water tank in the loft. Check that the tank has water and the supply is on. A stuck valve may be the cause if the tank is empty.
Then check the cylinder thermostat. If everything looks fine, the issue may be with the boiler or the pump. Call an engineer, since these parts need testing.
Electric immersion: no hot water
Look at the switch for the immersion heater, usually near the cylinder. Check it is on and the thermostat is set. A tripped fuse at the consumer unit can also cut power.
If the heater is on and the water stays cold, the element may have failed. An electrician or plumber can test and replace it. Do not open electrical parts yourself.
Tepid water but not hot: common across all systems
Lukewarm water can have several causes. A low thermostat setting is the easiest fix. Scale in the cylinder or boiler can also reduce heat, because it coats the heating parts.
Mixing valves and shower controls may be set wrongly. Because several faults feel alike, ask a plumber to check if simple steps fail. You can ask for a free quote and we will pass your details on.
Related guides and local help
If you want to know more, read How to Find a Reliable Plumber: 10 Things You Should Check. You can also read Hard Water and Your Plumbing: Effects, Costs and Solutions and How to Read Your Water Meter and Use It to Spot Leaks, because they cover closely related problems.
These guides help too: Bath vs Shower: Water Use, Running Costs and Drain Impact, Lead Pipes: Health Risks, How to Spot Them and Replacement, Leak Detection Cost Guide: What Changes the Price Most, Low Water Pressure: Causes, Diagnosis and Fixes in the UK and Leak Detection Methods: Acoustic, Thermal and Tracer Gas. Each one explains a related topic in plain English.
Need help near you? Read our plumbing help page first, or see Plumbing Repairs in Bulwell and Plumbing Repairs in Burgess Hill. You can also see Leak Detection in Dursley, since every service page has a free quote form. We pass each request to a local drainage engineer.
