No Heating Or Hot Water

What's happening?

When both heat and hot water disappear together, the fault is upstream of everything: the boiler is not firing, or it is firing and the pump is not moving water. A combi produces both from the same heat exchanger, so one fault takes out both. On a system or open-vented setup with a cylinder, losing both usually means the boiler itself, the programmer, or the power supply. The useful first split is whether the boiler shows any sign of life. A blank display points at power: a spur switch, a fuse, a tripped breaker. A display showing a fault code points at the boiler's own diagnostics. A display that looks normal but nothing gets warm points at the pump, a seized valve, or a control calling for nothing.

What usually causes it?

• System pressure below the boiler's minimum, so it locks out before firing
• A fault lockout the boiler will not clear until it is reset at the control panel
• The fused spur or boiler switch turned off, or a blown 3A fuse in it
• A programmer or timer that has lost its settings after a power cut and now calls for nothing
• A room thermostat with flat batteries, so the wireless receiver never gets a demand
• A seized circulating pump, or a motorised valve stuck in the wrong position
• A frozen condensate pipe in cold weather, shutting the boiler down on a specific fault code

Is it dangerous?

The loss of heat is not dangerous in itself, but a house with no heating in a hard frost is at risk of freezing pipes, and vulnerable or elderly occupants need warmth arranged the same day. Take it seriously and stop investigating if you smell gas, see water running from the boiler, or find scorching or a burning smell around it. Do not repeatedly press reset: most manufacturers say no more than two or three attempts, because each one puts more unburnt gas through the appliance.

Can I fix it myself?

Work through the free checks before you book anyone. Confirm the boiler has power at its switched spur. Read the pressure gauge: most systems run at about 1 to 1.5 bar cold, and below the marked band the boiler will refuse to fire. Check the programmer is on and set to the right day and time, and that the room thermostat is turned up and has fresh batteries. Note any fault code on the display, because it saves an engineer time and may tell you it is a frozen condensate you can thaw yourself. Reset once or twice, no more.

When should you call a heating engineer?

Call a heating engineer if the boiler locks out again after a reset, if the pressure will not hold when you top it up, or if you have a fault code the manual does not resolve. Call the same day in freezing weather or where anyone in the house is vulnerable. If the boiler is gas-fired, whoever attends must be Gas Safe registered, and any work on the gas or combustion side is theirs alone.

What will the heating engineer actually do?

• Read the fault history off the boiler and confirm the code against the manufacturer's manual
• Check the power supply, the spur fuse, and the wiring at the programmer, thermostat and wiring centre
• Test the circulating pump and the motorised valves for movement and correct switching
• Check and correct system pressure, then look for why it dropped
• Test the boiler's own safety devices, gas pressure and combustion where it is a gas appliance
• Recommission the system, prove heat to every radiator and to the hot water, and record the readings

Before you book anyone

1. Check the boiler has power at its switched fused spur.
2. Read the pressure gauge and note the figure.
3. Check the programmer is on and showing the correct day and time.
4. Turn the room thermostat well above room temperature and replace its batteries.
5. Write down any fault code shown on the boiler display.
6. Reset once. If it locks out again, stop and book an engineer.

Who fixes this

• Boiler repair
• Heating not working

Questions people ask

Sources & References

1. Vaillant: Most common boiler problems
2. Vaillant: How to reset a boiler
3. WaterSafe: Avoid a boiler breakdown