My boiler controller shows a flame (heating), but the boiler doesn't start: what should I do?

If your boiler controller shows a flame in Settings → Devices and the last communication time is recent, Snugr is indeed sending a heat request. The issue is then usually on the boiler side, its power supply, its circuit (gas/oil), or the wiring/control box.

Also check that the red hourglass icon (communication timeout) is not displayed. If it is, follow the dedicated communication error article first.

1) Boiler checks (independent of Snugr)

• Is the boiler properly powered and switched on?
• Is the water pressure correct? (refer to the boiler's manual)
• Are the fuses and circuit breaker OK (not tripped / not in safety mode)?
• Gas boiler: is the gas supply open?
• Oil boiler: is the tank not empty?

Tip: an indicator light or control screen (often behind a cover) should generally be lit if the boiler is powered. If nothing is lit, check the electrical panel and contact a professional if needed.

2) Check the Snugr boiler controller (mounting, contacts and wiring)

A. Check housing / base alignment

Make sure the housing is correctly positioned on its base: the electronic board's pins must be properly aligned with the wall part's connector.

B. Check the boiler contact wiring

The correct contact wiring is usually on:

• COM and NO (or on a terminal block named Boiler Contact depending on the installation)

Avoid COM and NC, except in very specific cases.

Reminder of meanings: COM: common · NO: normally open · NC: normally closed

3) Function test by forcing the control (if your model allows it)

Case A — Internal switch present (3 positions)

• AUTO: normal operation with Snugr
• OFF: forced off
• ON: forced on

Procedure:

1. Set the switch to ON.
2. Close the housing again.
3. Wait up to 2 minutes.

Interpretation:

• Boiler does not start in ON: issue independent of Snugr (boiler / power supply / safety / wiring). Contact a heating technician.
• Boiler starts in ON but not in AUTO: contact Snugr/4INCH support.

Case B — No internal switch (boiler contact test)

On some models, you can test the boiler's reaction by briefly connecting the two wires of the boiler contact: briefly connect the 2 wires connected to the COM and NO terminal block, or to the terminal block named Boiler Contact (depending on your installation).

Caution: never connect power wires (230V or others) together. If you are not sure which wires are involved, do not perform this test and contact a professional.

Interpretation: if the boiler starts when COM and NO (or Boiler Contact) are connected, but does not start during normal operation: contact Snugr/4INCH support for further diagnosis.

Who to contact and when?

• Boiler does not start even in forced mode (ON) or during the contact test: heating technician (issue independent of Snugr).
• Boiler starts in forced mode / contact test but not in AUTO/Snugr mode: Snugr/4INCH support.