Display normal but no heat to radiators

What is going on

The display is lit and normal, but the radiators stay cold. That usually means the boiler is not being asked to heat, or it is waiting on a setpoint or a priority, not that something has failed. Work through the display symbols and the parameters in order.

Likely causes

• No heat call from the thermostat or a thermostat wiring problem
• Outdoor temperature above the warm weather shutdown setting
• Supply temperature at or above the CH setpoint minus differential, so the boiler is waiting
• CH pump not running or not wired to terminals 7 and 8
• DHW call has priority and is holding off space heating

Check in this order

1. Look for the radiator symbol flashing during a thermostat call. If unsure, briefly short the thermostat terminals at the boiler with a jumper wire to see if the call registers, and remove it right after. Do not leave it in.
2. If the symbol does not show, read outdoor temperature (1.004) and compare to warm weather shutdown (2.025), because there is no heat call above that.
3. If flashing but not firing, compare supply temperature to CH setpoint (0.003). The boiler waits until supply drops below setpoint minus differential. Raise setpoint at 2.003 if too low.
4. Make sure the CH pump runs and is wired to terminals 7 and 8, and measure voltage at the pump during a call.
5. Radiator symbol steady and faucet symbol flashing means a DHW call has priority. Raise DHW setpoint (2.048) or shorten DHW priority time (2.043).
6. Check zone valves and flow by feeling the supply and return pipes for heat.

More boiler guides

• 0-10 VDC input to modulate firing rate (Mode 5)
• Annual maintenance and inspection
• Blank display
• Boiler pressure keeps dropping / FILL shows
• Boiler shows FILL and will not fire
• Cleaning the combustion side of the heat exchanger