No Hot Water but Heating Works? Causes & Next Steps

If your radiators are warm but the hot taps run cold, the problem is usually local to your hot water system rather than the whole boiler. A few quick checks can rule out simple issues, but anything involving gas, electrics or opening the boiler casing must be left to a qualified heating engineer.

Safety first, and when to call an engineer

If you smell gas, see scorch marks, or hear loud or unusual noises from your boiler, switch it off immediately and contact a Gas Safe engineer. Do not repeatedly reset the boiler if it keeps locking out, as this indicates a fault needing professional diagnosis.

Also, call an engineer promptly if you notice water leaking from the boiler, quickly dropping pressure, or exposed wiring around the boiler or cylinder. Ignoring these issues can lead to costly damage.

What you can check safely in 10 minutes

Before calling for help, check these simple things without tools or technical knowledge:

• Thermostat and programmer settings: Ensure hot water is set to "on" or "timed", not "off". For cylinders, set the thermostat above 55 °C.
• Boiler pressure gauge: Should be around 1.0 to 1.5 bar when cold. Near zero pressure can stop hot water from working.
• Boiler reset procedure: If safe and per your manual, try one reset using the reset button or control dial.
• Visible leaks: Look for drips, stains, or wet patches near the boiler, pipes, or cylinder.

If anything seems unsafe, do not touch it. Note any error codes or flashing lights on the boiler and share them with your engineer.

What not to do

Never remove boiler casing, adjust gas valves, or dismantle internal parts. Only Gas Safe registered professionals should do this work.

Do not bypass safety devices, bridge thermostats, or keep resetting a locking-out boiler. Avoid pouring hot water on condensate pipes or working on live wiring to programmers, pumps, or valves.

No hot water from a combi boiler

Combi boilers heat water on demand from the mains. If heating works but hot water doesn’t, the domestic hot water side usually has the fault.

Diverter valve stuck on heating

The diverter valve directs heat to radiators or taps. If stuck on heating, radiators warm but taps stay cold. An engineer must repair or replace the valve.

Plate heat exchanger scaling

Hard water in West Sussex can cause limescale build-up, reducing heat transfer and causing lukewarm or cold taps. Engineers can clean or replace the heat exchanger and suggest scale protection, especially if upgrading your boiler.

DHW sensors, low pressure, and condensate issues

Faulty domestic hot water sensors or thermistors can stop hot water demand being recognised. Low pressure or frozen/blocked condensate pipes can also cause problems, often with fault codes. Always check your manual for boiler fault codes and photograph the display before resetting.

No hot water, but heating works with a cylinder

With a hot water cylinder, the boiler heats stored water via a coil. Heating can work fine even if the cylinder side has a fault, leaving you with warm radiators but cold water.

Programmer, thermostats, and zone valves

Check that the hot water is scheduled on your programmer. Older units in Horsham and Billingshurst can easily be switched off by accident. The cylinder thermostat should be set correctly and firmly attached. A faulty thermostat or stuck zone valve can stop hot water flow without affecting heating.

Hot water cylinders and immersion heaters

Many cylinders have immersion heaters for backup. You can use these temporarily if safe and aware of extra costs. If the immersion trips or fails, the thermostat or element may need replacing. Older cylinders may lose heat quickly; upgrading to a modern or smart cylinder like a Mixergy unit can improve efficiency. Learn more on our hot water tank installation page.

Is it dangerous to have heating but no hot water?

Usually, this is inconvenient rather than dangerous. Faults like diverter valves or sensors rarely pose immediate safety risks. However, burning smells, repeated trips, loud banging, or water near electrics are serious warnings. Switch off and get a professional diagnosis if unsure.

Frequently Asked Questions

Why does my heating work but my hot water stays cold?

Common causes include a stuck diverter valve, faulty sensors, or issues with thermostats and zone valves.

Can I use my immersion heater if the boiler isn’t heating water?

Yes, as a temporary backup if it’s safe and you understand the higher running costs.

Is it dangerous to have no hot water, but the radiators are heating?

Usually no, but watch for burning smells, leaks, or unusual noises, which need urgent attention.

What can I safely check before calling a heating engineer?

Check thermostat settings, boiler pressure, reset the boiler once if safe, and look for visible leaks.

Next steps for West Sussex homeowners

If you’re in West Sussex, Horsham, Billingshurst, or nearby and have no hot water but heating works, an experienced engineer can quickly diagnose the fault. We test diverter valves, sensors, zone valves, and controls safely, then advise on repair or upgrades.

Pipeline Plumbing Services Ltd. offers fault finding, boiler repairs, and cylinder upgrades, including smart options. For older or unreliable systems, we can discuss new boiler installations or cylinder replacements.

To book a diagnosis or get advice, contact Pipeline Plumbing Services Ltd. or call 01903 740538. We’ll help get your hot water running again.