No Heating or Hot Water

If neither works, the boiler isn't producing heat at all — so the fault is upstream of the diverter valve. That points to the gas supply, ignition, flame-sensing, the pump, the PCB, a safety lockout, or system pressure. This is broader than a 'no hot water only' fault and usually needs an engineer, but a few safe checks can rule out simple causes first.

The most common causes when the boiler produces no heat for either system:

• • Ignition or flame-sensing failure — the boiler tries to light but can't, or can't confirm the flame, so it locks out (often shows a fault code).
• • Gas supply problem — a tripped gas meter, a prepayment meter out of credit, or a gas valve fault.
• • Low system pressure — below ~0.6 bar the boiler locks out for safety and won't fire.
• • Failed pump — the boiler fires but can't circulate water, so it overheats and shuts down.
• • PCB or electrical fault — the control board isn't sending the fire signal.
• • Tripped isolation / power cut — the boiler has no electrical supply.
• • Frozen condensate pipe — in cold weather, a frozen condensate can cause the boiler to lock out entirely.

Yes — one reset is safe and worth trying. Note any fault code on the display first, then press the reset button once. If the boiler re-fires and stays on, it may have been a transient lockout. If it locks out again, don't keep resetting — repeated lockouts mean a real fault, and cycling the boiler can stress components. Stop and book an engineer.

• • Pressure: if below 0.6 bar, top up to 1.2 bar via the filling loop (see our how-to-top-up guide), then reset.
• • Power: check the fused spur switch next to the boiler is on and the consumer unit hasn't tripped.
• • Programmer: confirm heating and hot water are set to 'on' or 'continuous', and the room thermostat is turned up above room temperature.
• • Gas: check another gas appliance (hob) works. If nothing gas works, contact your gas supplier before an engineer.
• • Fault code: write down any code on the display — it tells the engineer what to test before they arrive.
• • Cold weather: if the condensate pipe runs outside and it's below freezing, a frozen condensate can lock the boiler out. See our frozen condensate guide.

Anything inside the boiler casing — ignition, gas valve, flame sensor, pump, PCB — is gas work. Don't remove the casing, don't try to relight a pilot if the instructions don't resolve it, and never attempt gas-valve or combustion adjustments. If you suspect a gas smell or a gas supply problem, call the National Gas Emergency Service on 0800 111 999 immediately.

• • Read the fault code and confirm the lockout type (ignition, pressure, overheat, flame).
• • Test gas supply and gas pressure at the boiler.
• • Check ignition, flame-sensing electrode, and gas valve operation.
• • Verify system pressure and circulation (pump running, no airlocks).
• • Test the PCB for the correct fire signal and sensor inputs.
• • Inspect the condensate route for freezing or blockage in cold weather.
• • Re-commission and check safe combustion after any repair.

Yes — in freezing weather a frozen condensate pipe is one of the most common reasons a boiler locks out with no heating or hot water. The boiler detects the blocked condensate and shuts down to prevent flooding. If your condensate pipe runs outside and it's below freezing, this is a prime suspect. Our frozen condensate guide covers safe thawing and prevention.

No heating or hot water is the most common emergency we attend. Our Gas Safe Registered (594547) engineers respond 24/7 across Surrey, Berkshire, Buckinghamshire, and West London, carry common ignition, pump, and PCB parts for the major brands, and aim to restore heat and hot water in a single visit. Book online in 60 seconds or call us now.