What to Do When You Have Hot Water but No Central Heating?

What to Do When You Have Hot Water but No Central Heating?

Troubleshoot the Most Common Central Heating Faults with Confidence

You’re getting hot water from your taps, but your radiators stay cold. Frustrating? Definitely. But don’t panic—this is a very common issue and often one that can be diagnosed (and sometimes even fixed) quickly.

In this guide from A&C Heating and Plumbing Ltd., we’ll walk you through the possible causes, solutions, and when you should call in a Gas Safe engineer.

Check if the Radiators are Warm or Not

🚨 Quick Summary

Symptoms:
✔️ Hot water works normally
❌ Radiators are cold
❌ Central heating won’t turn on

Possible Causes:

  • Incorrect settings or timers

  • Faulty thermostat

  • Broken diverter valve

  • Air in the radiators

  • Low boiler pressure


🔍 Step-by-Step Troubleshooting Guide

1. ✅ Check Your Thermostat & Timer Settings

It may sound simple, but make sure:

  • The thermostat is set above room temperature (e.g. 20°C)

  • The heating program is actually ON

  • Smart thermostats (like Hive or Nest) are synced properly

🔧 Try temporarily switching to “manual” mode to test if your heating turns on.

Check the Boiler Pressure:

2. 🔁 Bleed Your Radiators

If your radiators are cold at the top but warm at the bottom, air is trapped inside.

🧰 Solution:

  • Use a radiator key to bleed each radiator

  • Let the air hiss out until water starts to flow

  • Re-pressurize the boiler if needed (see next step)


3. 🌡️ Check the Boiler Pressure

Most modern boilers (including Ideal, Worcester, Vaillant, Baxi) require pressure between 1.0–1.5 bar.

📉 If the pressure is too low:

  • Locate the filling loop

  • Open valves gently until pressure increases

  • Turn valves off at 1.2–1.5 bar

⚠️ Still no heating? Read on.


4. 🔀 Faulty Diverter Valve

This is a very common cause in combi boilers. The diverter valve switches heat between your hot water and central heating. If it’s stuck on hot water, you’ll have no heating.

🧰 Only a qualified engineer can test or replace the diverter valve.


5. 🔌 Reset the Boiler

Your boiler may have entered a fault or lockout mode.

🧯 Try this:

  • Turn the boiler off

  • Wait 30 seconds

  • Turn it back on and see if heating works

Look out for any fault codes (like F22, L2, F1), which can help identify the issue.


6. 🧠 Smart Thermostat Glitches

Smart thermostats sometimes lose connection with the boiler or Wi-Fi. Try:

  • Resetting your smart thermostat

  • Checking battery levels (if wireless)

  • Ensuring your app or hub is working properly


🧑‍🔧 When to Call a Heating Engineer

Call a professional if:

  • You’ve tried all basic checks

  • The diverter valve is faulty

  • There are persistent error codes

  • Your boiler makes unusual noises

  • There’s no heating after a reset

At A&C Heating and Plumbing Ltd., our Gas Safe registered engineers can quickly diagnose and fix these issues anywhere in North and West London.


📍 Areas We Cover:

🔹 North London:

Barnet, Finchley, Camden, Edgware, Kentish Town, Haringey, Enfield

🔹 West London:

Ealing, Acton, Chiswick, Brentford, Hounslow, Wandsworth, Brent


🛠️ We Work With All Major Boiler Brands:

  • ✅ Ideal

  • ✅ Vaillant

  • ✅ Worcester Bosch

  • ✅ Baxi

  • ✅ Glow-worm

  • ✅ Ferroli


📞 Book a Central Heating Repair Today

Whether it’s a diverter valve, pressure issue, or faulty thermostat, we’ll get your heating running again—fast.

📲 Call Now: 0779 559 5757
🕒 Same-day appointments available
🚨 Emergency heating engineers in London