Error E01: No Signal from Boiler

Symptoms

• The T1 display shows error code E01 with the message "No signal from boiler"
• The thermostat calls for heat but the boiler does not fire
• The flame icon on the T1 does not appear when the target temperature is above the room temperature
• The app shows "Heating: Waiting for boiler response" indefinitely

Likely Causes

1. Loose or disconnected wiring between the T1 wall plate and the boiler terminals. A wire may have come loose during installation or from building vibration.
2. Boiler interlock or lockout — the boiler itself may be in an error state and unable to respond to a call for heat, independent of the thermostat.
3. Call-for-heat relay fault — the T1's internal relay may not be switching correctly, or the relay wiring (COM/NO terminals) has a break in the circuit.
4. OpenTherm bus failure — if using OpenTherm, the OT+ / OT- wiring may be damaged or the boiler's OpenTherm board may have failed.
5. Boiler power supply issue — the boiler may not be receiving mains power (tripped breaker, blown fuse, or faulty spur).

Step-by-step Fix

1. Check the boiler is powered on. Look at the boiler's own display or indicator lights. If the boiler is completely dark, check the circuit breaker or fused spur switch that supplies it. Reset if tripped.
2. Check for a boiler lockout. If the boiler displays its own error code (e.g., a flashing light or fault number), it may be in lockout. Refer to the boiler manufacturer's manual to clear the fault — most boilers have a reset button. Common causes include low gas pressure, ignition failure, or overheating.
3. Inspect the wiring at the T1 wall plate. Switch off power at the breaker first. Remove the T1 from the wall plate and check that all wires are firmly seated in their terminals. Pay particular attention to the COM and NO terminals (relay mode) or the OT+ and OT- terminals (OpenTherm mode). Re-tighten any loose screws.
4. Inspect the wiring at the boiler end. With the power still off, check the corresponding terminals on the boiler's wiring centre or PCB. Ensure wires are secure and not corroded. Look for signs of heat damage or melting on connectors.
5. Test circuit continuity. Using a multimeter set to continuity mode, test the cable run between the T1 wall plate and the boiler terminals. Place one probe on the T1 COM terminal wire and the other on the boiler end of the same wire. A continuous tone confirms the wire is intact. Repeat for NO (or OT+/OT-). If there is no continuity, the cable is damaged and must be replaced.
6. Test the T1 relay directly. Restore power and navigate to Settings > Installer > Test Mode (PIN: 1234). Tap Relay ON. You should hear a faint click from the T1 as the relay closes. If no click is heard, the relay may be faulty — contact Monverta support for a replacement unit.
7. Reset the boiler and thermostat. Power off both the boiler and the T1 (at the breaker). Wait 60 seconds, then restore power to the boiler first, followed by the T1. Allow 2 minutes for the T1 to re-establish communication. Check whether E01 has cleared.