Why has my boiler got hot water but no heating?
Hot taps but cold radiators usually means the boiler is fine and a control or a valve is at fault. Here is what to check, and the part that most often causes it.
Gas Safe Registered · 587401
Manufacturer Approved
Fully Insured
Same-Day Service
Local Engineers
Upfront cost — no obligation If your taps run hot but the radiators stay cold, the problem is almost always inside the boiler or its controls rather than the boiler being broken outright. The most common cause is a stuck diverter valve, but a faulty thermostat, a timer set wrong, low pressure or closed radiator valves can all leave you with hot water and no heating. This guide walks through what to check yourself and when to call an engineer.
Why do I have hot water but no heating?
When you have hot water but no heating, it usually means the boiler itself is working — it is just not sending heat to the radiators. The usual causes are a stuck diverter valve (the part that switches the boiler between heating and hot water), a faulty or flat-battery room thermostat, a programmer or timer set to the wrong mode, low boiler pressure, or radiator valves that have been turned down or airlocked. Working through these in order usually points to the cause.
When you have hot water but no heating, it usually means the boiler itself is working — it is just not sending heat to the radiators.
Quick checks you can do yourself
Before calling anyone, run through a few simple checks. Make sure the programmer or timer is set so the heating is on and calling for heat. Check the room thermostat — turn it well above the current room temperature, and replace the batteries if it is a wireless model. Look at the boiler pressure gauge; if it is below 1 bar, low pressure may be stopping the heating, and our boiler pressure guide explains how to top it up. Finally, check that your radiator valves are open, and bleed any radiators that are cold at the top but warm at the bottom.
Before calling anyone, run through a few simple checks.
The most likely culprit: a stuck diverter valve
If the controls and pressure are all fine, the most likely cause is a stuck diverter valve. This valve directs hot water either to your taps or to your radiators. When it sticks or wears out, the boiler often defaults to hot water — so the taps stay hot while the heating gets nothing. A diverter valve is an internal boiler part, so freeing or replacing it is a job for a Gas Safe engineer rather than a DIY fix.
If the controls and pressure are all fine, the most likely cause is a stuck diverter valve.
When should I call a Gas Safe engineer?
If you have checked the thermostat, the timer, the pressure and the radiator valves and still have no heating, it is time to call an engineer, as the fault is likely inside the boiler. Our Gas Safe engineers can diagnose a stuck diverter valve, a faulty pump or a control fault and get your heating back on — see our boiler repair service. If it is cold and there is a baby, an elderly person or someone unwell in the home, treat it as urgent.
If you have checked the thermostat, the timer, the pressure and the radiator valves and still have no heating, it is time to call an engineer, as the…
Frequently Asked Questions
Why is my water hot but radiators cold?
It usually means the boiler is working but not sending heat to the radiators. The most common cause is a stuck diverter valve, though a faulty thermostat, a wrong timer setting, low pressure or closed radiator valves can also be to blame.
What is a diverter valve?
A diverter valve is the part inside a combi boiler that switches the flow of hot water between your taps and your radiators. When it sticks, the boiler often defaults to hot water, leaving you with no heating.
Can I fix no heating but hot water myself?
You can check the simple things — the thermostat, the timer setting, the boiler pressure and the radiator valves. If those are all fine, the fault is usually inside the boiler and needs a Gas Safe engineer.
Is it an emergency if I have hot water but no heating?
Not usually, as you still have hot water. But if it is cold weather and there is a baby, an elderly person or someone unwell in the home, it is worth getting it seen quickly.
What Our Customers Say
Rated 5 stars by homeowners and landlords across East London
“Boiler installation completed on time.”
Mohammad Kabir | Canary Wharf, East London
“Gas safety checks for properties.”
Jay Alam | Ilford, East London
“Cooker installation, gas safety check and boiler check.”
Azizul Chowdhury | Dagenham, Essex
Get a Free Quote
Fill in the form and we'll call you back as soon as possible
Quick Booking
📞 We'll call you back
Why Choose Gas First Ltd?
Professional, reliable, and certified gas engineering services across East London
Gas Safe Registered
All work carried out by fully certified Gas Safe engineers
Fast Emergency Response
Quick attendance for urgent gas & heating issues across East London
Transparent Pricing
Fair quotes with no hidden charges — you know the cost upfront
5-Star Customer Service
Rated highly by homeowners & landlords across East London
Experienced Local Engineers
Skilled team covering all East London boroughs
Domestic & Commercial
Services for homes, rentals, and businesses
Areas We Cover
We provide gas, boiler, and plumbing services across East London and nearby areas.
Need a Reliable Gas Engineer in East London?
Contact Gas First Ltd today for fast, professional gas, boiler, and plumbing services across East London.