No heating · Combi · Obvious once you look
Wireless receiver relay failed
“Hot water's fine but the radiators are stone cold, whatever I do with the thermostat.”
In short
Hot water works; central heating does not. The receiver has power and shows a demand, but its relay never passes the live to the boiler.
What the customer says
- “Hot water's fine but the radiators are stone cold, whatever I do with the thermostat.”
- “We've got hot taps but no heating at all since yesterday.”
- “The thermostat shows the flame and the receiver light's on.”
The boiler has power and the thermostat is calling, so the fault is between them: wireless thermostat -> receiver -> boiler.
How to find it in the simulator
If this is your home: this page is written for heating engineers. Mains wiring and gas appliances are not DIY jobs; call a Gas Safe registered engineer. If you smell gas, leave the building and call the National Gas Emergency Service on 0800 111 999.
In the simulator the meter is safe. On a real system: isolate and prove dead before you touch a terminal, and make live tests only if you are trained and equipped for them. The steps below are the method as practised in the simulator, in its own words, for competent persons and for learners under the supervision of one.
- 01
CONFIRM the complaint yourself: spur ON, run the simulation, ask for heating only, then hot water only. Watch the valve(s), boiler and pump.
- 02
The heating demand travels: wireless thermostat -> (radio) -> receiver -> wire -> boiler RT terminal.
- 03
Does the RECEIVER show the demand? Then the thermostat and its pairing are proven.
- 04
Meter the receiver: L to neutral (its supply), then its OUTPUT terminal to neutral.
- 05
Output live at the receiver? Then meter the boiler's RT terminal.
- 06
The fault lies between the LAST point with 230 V and the FIRST without.
- 07
ISOLATE (stop the simulation) before you touch anything. Continuity only on a dead circuit.
- 08
Click Report Fault, then the wire or part you have PROVEN faulty.
What the meter shows
Where to probeStat calling, receiver showing HEATING: meter the receiver's L to neutral, then the receiver terminal that feeds the boiler.
The readingYou are looking for a device with 230 V going IN and 0 V coming OUT at a moment when it should be passing the live on.
The faultThe receiver has power and shows a demand, but its relay never passes the live to the boiler.
Common wrong guesses
Receiver display shows HEATING, its output terminal reads 0 V. Verdict?
- Boiler fault
- Thermostat batteries
Show the right answer
Receiver relay failed
The demand was received (so the stat and pairing are fine) but the relay output is dead.
Related
More no heating faults
Components involved
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