No Hot Water But Heating Works In Croydon?
If the radiators are warming up but the taps are cold, the boiler may not be switching into hot water mode properly.
If you have no hot water but heating works, the boiler is not completely dead. That is the confusing part. The radiators come on, the boiler fires, but when you open the tap you either get cold water, lukewarm water, or hot water that disappears after a few seconds.
We see this a lot on combi boilers around Croydon, especially in flats near East Croydon, older homes off London Road, and family houses in Addiscombe where the boiler has been working hard through winter.
MPS Heating & Plumbing LTD helps homeowners across Croydon, Thornton Heath, Norbury, South Croydon, West Croydon, Selhurst and East Croydon diagnose hot water faults properly, without guessing at parts.
If your heating is working but there is no hot water from the boiler, call 0203 576 6769 and we can talk through what is likely happening before you book a visit.
Why The Heating Can Work But The Hot Water Fails
With a combi boiler, heating and hot water are controlled in different ways. Your radiators can still heat up because the boiler is able to fire and send water around the heating circuit. But when you turn on a hot tap, the boiler has to detect that demand and switch priority over to hot water.
That switch-over is where the fault often sits. It might be the diverter valve sticking, the flow sensor not detecting water movement, a thermistor giving the wrong reading, or the plate heat exchanger being restricted by scale and sludge.
London hard water does not help. Over time, scale can build up inside plate heat exchangers, especially on older combi boilers in tight cupboards where servicing has been missed or rushed.
If the boiler has not had a proper recent check, our boiler servicing checks for Croydon homes can help spot wear, scale signs, pressure issues and safety problems before they turn into repeat breakdowns.
Common Reasons For No Hot Water When The Heating Still Works
| Possible Fault | What It Usually Looks Like |
|---|---|
| Diverter valve sticking | The boiler fires for heating, but does not properly switch over when a hot tap is opened. Sometimes the radiators warm when you are trying to run hot water. |
| Blocked plate heat exchanger | Hot water may start warm, then go cold, or only work at a slow tap flow. Scale and sludge can restrict heat transfer inside the boiler. |
| Flow sensor fault | The boiler may not realise a hot tap has been opened. You might hear nothing from the boiler when you turn the tap on. |
| Thermistor or temperature sensor issue | The boiler may read the water temperature wrongly, causing unstable hot water or the burner to cut in and out. |
| Low pressure or system fault | Some boilers stop hot water performance when the pressure is too low or there is another fault code showing on the display. |
The Boiler Is Working, Just Not In The Way You Need
A lot of people say, “The boiler can’t be broken because the heating works.” Fair thought. But on a combi boiler, heating working does not prove the hot water side is healthy.
We had one job near East Croydon where the radiators were fine every evening, but the shower would go hot, cold, hot, then cold again. The customer thought it was the shower valve. It was not. The boiler was struggling to transfer heat properly when the tap demand changed.
On another call in Norbury, the boiler fired perfectly for heating but did almost nothing when the kitchen tap opened. That pointed more toward the boiler not detecting hot water demand, not a general heating failure.
The pattern matters. Hot then cold is different from no response at all. Lukewarm water is different again.
Hot Water Goes Hot Then Cold
This can happen when the plate heat exchanger is restricted, the boiler is overheating then cutting back, or the hot water temperature readings are unstable. It needs proper checking, not just turning the temperature dial up.
Boiler Does Nothing At The Tap
If the boiler does not react when you open a hot tap, the flow sensor or hot water demand side may be the issue. The boiler may not know you are asking for hot water.
Radiators Warm During Hot Water
If radiators start warming while you are running a hot tap, the diverter valve may not be sending heat where it should. This is a common combi boiler fault.
What You Can Check Before Calling
Start simple. Check the boiler display for an error code. Check the pressure gauge if your boiler has one. Make sure the hot water temperature has not been turned right down by accident. Try more than one tap, because one faulty tap or shower can confuse the diagnosis.
If every hot tap has the same problem, and the heating still works, the issue is more likely around the boiler’s hot water controls, diverter valve, flow sensor or heat exchanger. If only one shower is affected, that might be a shower valve or local plumbing issue instead.
If you are in Croydon and the taps have suddenly gone cold while the heating still comes on, call 0203 576 6769. We will ask what the boiler does when the tap opens before we tell you what is likely.
No Guesswork
We check the boiler response at the tap, hot water flow, temperature behaviour, fault codes, pressure, visible leaks and whether heat is being sent the wrong way through the system.
Straight Advice
If it is a small part or control issue, we say so. If scale, sludge or a blocked plate heat exchanger is likely, we explain what that means before any work goes ahead.
Local Experience
MPS Heating & Plumbing LTD is Gas Safe Registered — ID 662170, working across Croydon on Worcester Bosch, Vaillant, Ideal and Baxi combi boilers.
When It Needs An Engineer
If the heating works but there is no hot water, the repair cost depends on what has failed. A sensor fault is different from a sticking diverter valve, and a scaled-up plate heat exchanger is different again.
We do not invent a price before checking the boiler. We diagnose the fault, explain what we have found, and quote before repair work starts. If the boiler needs repair rather than a service, we will tell you clearly.
Real Google Reviews From MPS Customers
“Ansar is a true professional that takes pride in his work. His service is excellent, efficient and the site left clean and tidy. After completing 20+ jobs for my management business, I can highly recommend him.”
— James Hutton“Ansar certainly knows his stuff. He was meticulous in his approach to dealing with a problem I had with my Worcester…”
— desdemona fairchild“Brilliant! Prompt and no hassle – highly recommended. Ansar was great, professional and communicative. He talked us through what was happening, why and how long it would take. He then delivered on time.”
— Ellis Cain-JonesNo Hot Water But The Heating Still Comes On?
If you are in Croydon, East Croydon, Thornton Heath, Norbury, Addiscombe, Selhurst, South Croydon or West Croydon, MPS can check why the boiler is not switching into hot water mode properly.
When you call, we will ask whether the boiler fires at the tap, whether the water goes hot then cold, whether the radiators warm up during hot water use, and whether any fault code is showing.
No Hot Water But Heating Works FAQs
Why do I have heating but no hot water?
On a combi boiler, the heating side can still work even if the hot water side has a fault. Common causes include a sticking diverter valve, a faulty flow sensor, a blocked plate heat exchanger, or a temperature sensor issue.
Could it be the diverter valve?
Yes. A diverter valve sends heat either to the radiators or to the hot water side. If it sticks or fails, the boiler may heat the radiators but not send heat properly to the taps.
Why does my hot water go hot then cold?
Hot water that keeps cycling hot and cold can point to restricted flow, scale inside the plate heat exchanger, unstable temperature readings, or the boiler cutting back because it cannot transfer heat properly.
Can London hard water cause this?
It can contribute. Hard water can scale up parts of the hot water side over time, especially the plate heat exchanger on older combi boilers. Sludge from the heating system can also make the issue worse.
What should I check before booking a repair?
Check whether all hot taps are affected, whether the boiler display shows an error code, whether the pressure is low, and whether the boiler reacts when you turn a hot tap on. Do not remove the boiler casing or try to work on gas-side parts.