Boiler: No Hot Water

No hot water is miserable – especially in winter. Before you panic, there are a few things you can check yourself. Some fixes are simple; others need a Gas Safe registered engineer.

Quick Checks You Can Do

1. Check the Boiler Display

What does the boiler display show?

• Normal/on: Boiler thinks it's working
• Error code: Note it down – tells us what's wrong
• Blank/off: Power issue

2. Check the Pressure Gauge

Low pressure is the most common cause of boiler problems.

Healthy pressure: 1.0 - 1.5 bar when cold

Too low (below 1 bar)? You can top this up yourself. See our guide: How to repressurise your boiler

Too high (above 2.5 bar)? Pressure relief valve may have opened. You'll need to bleed a radiator to reduce pressure.

3. Check the Thermostat

Room thermostat:

• Is it set high enough to call for heat?
• Are the batteries dead?
• Is it in the right mode (heating/hot water)?

Boiler thermostat:

• Is the temperature dial turned up?
• Is the timer set correctly?

4. Check for a Frozen Condensate Pipe

In cold weather, the condensate pipe (a small plastic pipe that goes outside) can freeze, shutting down the boiler.

Signs:

• Boiler locks out in very cold weather
• Gurgling sounds from boiler
• Error codes related to blockage

How to thaw:

1. Locate the condensate pipe (usually runs outside)
2. Pour warm (not boiling) water over the frozen section
3. Reset the boiler once thawed

5. Reset the Boiler

If there's an error code, try a reset:

1. Find the reset button (often marked with a flame or "reset")
2. Press and hold for 3-5 seconds
3. Wait for the boiler to restart

If it keeps locking out, don't keep resetting – there's an underlying fault that needs diagnosis.

Common Faults Requiring an Engineer

Faulty Diverter Valve

In combi boilers, the diverter valve switches between heating and hot water. If it sticks, you'll have heating but no hot water (or vice versa).

Signs:

• Heating works, hot water doesn't
• Radiators get hot when you run taps

DIY fix? No – internal component.

Repair cost: From £200-300

Broken Pump

The pump circulates water through the system. If it fails, water won't flow to taps or radiators.

Signs:

• Boiler fires but radiators stay cold
• No flow noise
• Hot water tap pressure reduced

DIY fix? No.

Repair cost: From £200-350

Ignition Failure

The boiler won't light if the ignition system fails.

Signs:

• Boiler tries to start but doesn't fire
• Clicking sounds
• Error codes mentioning ignition

DIY fix? No – involves gas components.

Repair cost: From £150-250

Faulty PCB (Control Board)

The PCB is the boiler's brain. When it fails, anything can go wrong.

Signs:

• Random error codes
• Intermittent operation
• Display issues

DIY fix? No.

Repair cost: From £300-500

Heat Exchanger Blocked or Failed

Scale buildup or a failed heat exchanger means water can't be heated efficiently.

Signs:

• Lukewarm water only
• Strange noises (kettling)
• Gradual decline in performance

DIY fix? No.

Repair cost: From £400-700 (sometimes not economical on older boilers)

When to Call an Engineer

Call a Gas Safe engineer if:

• The boiler keeps locking out after reset
• There are error codes you can't clear
• You smell gas
• Pressure drops repeatedly (indicates a leak)
• Any internal repair is needed

Why You Need Gas Safe

All boiler repairs involving gas or internal components must be done by Gas Safe registered engineers. It's the law, and it's for safety.

All Flash Team boiler engineers are Gas Safe registered. You can verify any engineer's registration at GasSafeRegister.co.uk.

Get a Quote

Contact us for a no-obligation quote on boiler repair. We'll diagnose the problem and give you honest advice on repair vs replacement.