No Hot Water But Heating Works? Here’s What Could Be Wrong

Heating On But No Hot Water – What’s Going On?

You're getting central heating and your radiators are warm — but your taps and shower are running cold. If this sounds familiar, you’re not alone. “No hot water but heating works” is one of the most common boiler issues we’re called out to fix across Wokingham, Reading, Ascot, and the surrounding Berkshire area.

At Lucas Plumbing & Heating Ltd, we diagnose and repair boiler faults quickly — often the same day. Here’s what might be causing the problem and how we can help.

Common Causes When Heating Works but There’s No Hot Water

 1. Faulty Diverter Valve (Combi Boilers)

In combi boilers, a diverter valve switches between heating your radiators and supplying hot water. If it’s stuck or broken, it may only be heating your central heating circuit — leaving you with cold taps.

Signs:

• Heating works, but no hot water
• Tap runs cold even when heating is on
• Boiler makes noises but no water is heated

 Fix: Replace or repair the diverter valve (a common service call-out for our team).

2. Airlock in Pipes or Hot Water System

Air trapped in the hot water system can prevent flow, even if the boiler is working correctly.

Signs:

• Intermittent hot water
• Cold water flow is fine, but hot water has little pressure or no flow

Fix: We can bleed the system or clear the airlock to restore proper flow.

3. Thermostat or Cylinder Sensor Fault (System Boilers)

If you have a system boiler with a hot water cylinder, the issue might be a faulty cylinder thermostat or temperature sensor that isn't telling the boiler to heat the water.

Signs:

• Water in cylinder stays cold
• Heating timer is working but cylinder never warms

 Fix: Replace thermostat or check wiring to restore functionality.

4. Boiler Pressure Too Low

Low pressure can stop the boiler from firing properly for hot water, even if the heating circuit still works.

Signs:

• Pressure gauge below 1.0 bar
• Error code flashing
• Water dribbles or doesn't heat up fully

 Fix: We’ll check for leaks, top up pressure, and test expansion vessel integrity.

 5. Broken Motorised Valve (Y Plan or S Plan Systems)

In older setups with separate hot water and heating zones, motorised valves direct flow to the right part of the system. A faulty actuator may leave heating working but block hot water flow.

Signs:

• Heating and hot water controls are separate
• One zone not functioning
• Valve motor is unresponsive or noisy

 Fix: Replace the motor head or valve body.

6. Timer or Programmer Settings Incorrect

Sometimes the cause is simple: your heating is scheduled but hot water isn’t. Check that your programmer or smart thermostat has hot water enabled.

Signs:

• No hot water at expected times
• Programmer shows heating ON, but hot water OFF

 Fix: We’ll check and update your settings or install a modern controller if needed.

7. Frozen Condensate Pipe (In Winter)

In freezing weather, the condensate pipe can block — stopping the boiler from producing hot water, especially during high demand.

Signs:

• Gurgling noises
• Error code (often F28 or similar)
• No hot water but heating occasionally works

 Fix: Defrost the pipe safely and insulate it to prevent future problems.

How Lucas Plumbing & Heating Ltd Can Help

We provide fast, professional diagnosis and repair of:

• Combi, system, and conventional boilers
• Vaillant, Worcester, Ideal, Baxi, and more
• Smart thermostats and control systems
• Hot water cylinders and valves

Our engineers are Gas Safe Registered, fully insured, and cover Wokingham, Reading, Ascot, and surrounding areas.

Typical Repair Costs

Estimated Cost (incl. labour)Diverter valve replacement £120–£300

Airlock clearance £70–£100

Cylinder stat replacement £85–£150

Motorised valve replacement £140–£320

Pressure top-up and leak test £60–£100

We always provide transparent quotes with no hidden charges.

No Hot Water? Let’s Get It Fixed

Don’t let cold showers ruin your day. If your heating works but your hot water doesn’t, Lucas Plumbing & Heating Ltd is just a call away.

📲 Call us on  01184371679

Request a quick boiler check at  www.lucasplumbing.co.uk

We offer same-day visits when possible and emergency appointments throughout Berkshire.