If you have hot water but no heating, check several things before calling an emergency boiler engineer. Your boiler is likely working, but the issues might be within the parts of the system that send heat to your radiators, not the boiler itself. It could be a circulation issue, a stuck valve or a control setting, and luckily, you can check many of these issues yourself in just a few minutes.
In this guide, we explore the common causes of hot water but no heating, the fixes you can try at home and when you need to call a Gas Safe registered engineer.
Working hot water, no heating: Summary
| What you are seeing | Likely cause | What to do | DIY or pro? |
| Radiators cold, hot water fine | Thermostat or timer set wrong | Check the settings and schedule | DIY |
| One or two radiators cold at the top | Trapped air | Bleed the radiator | DIY |
| Radiators patchy or cold at the bottom | Poor circulation or sludge | Balance or power flush | Pro |
| Pressure gauge below 1 bar | Low boiler pressure | Top up via the filling loop | DIY |
| Taps hot but no radiators at all (combi) | Stuck diverter valve | Engineer replaces the valve | Pro |
| No heating after cold snap, boiler gurgling | Frozen condensate pipe | Thaw the pipe | DIY if the pipe is accessible. Pro if it is not. |
| Nothing works after all the above | Pump or internal fault | Engineer inspection | Pro |
Why do I have hot water but no heating?
If your taps are running hot but your radiators stay cold, it proves the boiler is still firing and heating water. This means that the problem is often further along the system. It could be in the controls that tell the heating when to activate, the circulation that sends the water around the radiators or the valve that determines whether hot water should go to taps or radiators.
It can be intimidating fixing problems like this yourself, and that’s understandable, but in this case, the fix can be quite simple. Your home can be warm again, but don’t assume DIY fixes are always the case. If you try the quick fixes and nothing happens, you might need professional intervention. We’ve listed the checks below in order, from the quick wins to those that need a specialist.
How to fix hot water but no heating
Check your thermostat and heating settings
Begin with this. It is one of the quickest and easiest things to rule out. Check that the heating is switched on and that any timer is showing it should be warming up the house now. Set the temperature a few degrees above the current room temperature. This will give the boiler a reason to fire up.
Check that your thermostat is turned up and that the batteries aren’t flat in wireless models. Then check the boiler’s flow temperature (your user manual will show you how to do this). It should be around 60C°-70°C. If the flow temperature is set too low, it may not get the water warm enough to heat the radiators.
Check and bleed the radiators
If some radiators appear warm at the bottom but cold at the top, that’s trapped air. Bleeding a radiator should fix this. Turn the heating off, hold a cloth under the bleed valve and open it with a bleed key until the hissing stops and water appears. Then close it.
If the entire radiator is cold, or the heat is patchy across the house, it’s likely that you have a circulation problem or sludge in the system. This often needs a power flush for optimal results and is best left to a central heating engineer in London. The system may also need balancing. You can do this yourself, but if you are unsure, ask your engineer, and they will do it for you.
Check the boiler pressure
A look at your pressure gauge will soon tell you if this could be the issue. When the system is cold, the boiler should sit at around 1 to 1.5 bar. This can vary by boiler type, so always check the user manual for the figures for your boiler.
If the needle is below 1, low pressure could be what’s stopping your heating from working. You can restore the pressure to its correct level by using the filling loop. If the pressure keeps falling after doing this, there is often a bigger problem to investigate. Our guide to why your boiler keeps losing pressure explains the common issues and what you can do.
Could it be the diverter valve?
If you have a combi boiler and your taps are hot but the radiators just don’t heat up, a stuck diverter valve is normally to blame. The diverter valve decides where to send the hot water, prioritising the taps when you run them. If it gets stuck, you’ll have endless hot water, but no heating.
You can’t fix this yourself. You’ll need a Gas Safe registered engineer in London to test the valve and replace it if necessary.
Is the condensate pipe frozen?
In cold weather, the condensate pipe can freeze, causing the boiler to fail to work properly or shut down altogether. As this pipe carries water to an outside drain, it can freeze where it runs outside.
You can often thaw it yourself by holding a hot water bottle or a cloth soaked in warm water against the pipe. Do not use boiling water! Applying warm water should clear the flow, but if it doesn’t and the pipe keeps freezing, ask an engineer to insulate it or re-route it.
What if you have heating but no hot water?
If your heating works but no hot water comes from the taps, the problem is less likely to do with the heating circuit and more likely the hot water side of the system. This could involve other investigations and work, so speak to a professional for extra guidance.
When should you call a professional central heating engineer?
If you have worked through the checks we’ve mentioned and your heating still won’t come on, the fault is likely something behind the boiler cover. In many cases, it’s a faulty pump, but it can often be other parts hidden behind the cover.
A job like this is only for a qualified professional. At no stage should you attempt to remove the cover or try to repair any internal parts. At London Property Services, our Gas Safe registered engineers cover the whole of London 24/7. We can dispatch an engineer for emergency boiler repairs in London quickly so you can get your heating back to how it should be. Contact us today to book your engineer or get a free quote.
