If your taps run hot but the radiators stay cold, the boiler itself is usually working. The problem is more often in the controls, or in the valve that sends hot water to the radiators instead of the taps. Start with the simple checks: the timer, the room thermostat and the radiator valves. If they’re all fine, it’s likely a part such as a diverter valve, zone valve or pump that needs a Gas Safe registered engineer. It’s one of the most common winter calls we get for boiler service and repairs, from Aylesbury to the villages around it.
Why you can have hot water but no heating
Your boiler heats water for two jobs: your taps and your radiators. Something has to decide where that hot water goes.
- With a combi boiler, a diverter valve inside the boiler switches between heating and hot water. If it sticks in the hot water position, the taps work but the radiators don’t.
- With a system or regular boiler and a cylinder, motorised zone valves on the pipework open and close to send heat to the radiators or the cylinder. If the heating valve fails, the cylinder still heats up but the radiators don’t.
Either way, the boiler is firing, so it’s easy to assume the boiler is fine and the radiators are the problem. In fact it’s usually something in between.
Safe checks you can do yourself
Before calling anyone, work through these:
- Check the timer or programmer. Make sure the heating channel is on, not just hot water, and that the clock is correct after any power cut.
- Turn up the room thermostat. Set it a few degrees above the room temperature. If it’s battery powered or wireless, try fresh batteries.
- Look at smart controls. If you have an app-controlled thermostat, check it’s online and not in holiday or away mode.
- Check the radiator valves. Make sure the TRVs aren’t turned right down. A TRV that has been off all summer can stick, so try turning it fully open.
- Check the boiler pressure. On a sealed system, the gauge usually sits around 1 to 1.5 bar when cold. Check your manual for your boiler’s figure.
If these all look right and the radiators are still cold, stop there. Our heating controls page explains the types of controls we fit and repair.
Faults that need an engineer
Once the simple checks are done, the likely causes are:
- A stuck or failed diverter valve in a combi boiler.
- A faulty motorised zone valve or its actuator head on a system with a cylinder.
- A failed or sluggish pump, which may still move enough water for the cylinder but not the radiators.
- A wiring or control fault, so the thermostat isn’t actually telling the boiler to heat.
- Sludge or air stopping water reaching the radiators properly.
These involve the boiler internals or the system wiring, so they’re not DIY jobs. Leave the boiler casing on and call a Gas Safe registered engineer. If you ever smell gas, turn off the supply at the meter if you can, open the windows and call the National Gas Emergency Service on 0800 111 999.
Heating faults across the Chilterns
Homes around the Chilterns vary a lot. Newer estates near Aylesbury mostly have combi boilers, while older cottages and larger family houses in Amersham, Chesham and Great Missenden are more likely to have a hot water cylinder, zone valves and more complicated controls. That makes the cause a little different from house to house, but the first checks above apply to all of them. Hard water across much of the area can also add to wear on valves and pumps over time.
Frequently asked questions
Why are my radiators cold but my hot water works?
Usually because the hot water from the boiler isn’t being directed to the radiators. On a combi this is often a stuck diverter valve. On a system with a cylinder it’s often a faulty zone valve. Check the timer, thermostat and radiator valves first. If they’re fine, an engineer will need to test the parts.
Can a thermostat cause no heating but hot water?
Yes. If the room thermostat isn’t calling for heat, the boiler will only heat your hot water. Flat batteries, a wireless receiver that has lost its connection or a thermostat set too low are all common causes. Turn it up a few degrees and replace the batteries before booking a repair.
Is it safe to keep using the boiler with no heating?
If the boiler is running normally for hot water, isn’t leaking or showing a fault and there’s no smell of gas, it’s generally fine to keep using it for hot water while you arrange a repair. If anything seems wrong, switch it off and get it checked by a Gas Safe registered engineer.
Radiators still cold?
Give us a call on 01296 425 424 or drop us a message and we’ll come out, find out why your heating isn’t coming on and get your radiators warm again.