Start here — the 10-minute checklist
Before anything else, verify in order:
- Thermostat: HEAT mode, temp set ABOVE current room temp. Display on (dead batteries = no signal).
- Power: boiler emergency switch ON. Breaker not tripped.
- Gas: gas valve at boiler is open. Other gas appliances working? If they're not, it's a gas-supply issue, not a boiler issue.
- Pressure: gauge reads 12-20 PSI cold. Below 5 PSI = low-water lockout.
All four check out and still no fire? Work through the 7 causes below.
The 7 reasons (in order of frequency)
1. Thermostat issue (30%)
Dead batteries, wiring issue, miswired smart thermostat. Test: jump R and W terminals at the thermostat — if the boiler fires, the thermostat is the problem.
2. Low water / pressure lockout (20%)
Pressure dropped below the cutoff threshold. Boiler refuses to fire as safety. Refill to 12-15 PSI. If it drops again within hours, there's a leak — see our leak guide.
3. Ignition failure (15%)
Igniter dirty/failed, flame rod fouled. Often signaled by lockout code on display. Common service item — same-visit fix in most cases.
4. Gas valve failure (10%)
Valve fails closed. No fuel to burner. Diagnosed with manometer. Routine replacement.
5. Blocked or frozen condensate line (8%)
Mod-con boilers produce acidic condensate. Frozen or clogged line triggers safety lockout. Common in Park City/Heber during cold snaps. Fix: thaw, then heat-trace or relocate.
6. Tripped high-limit (8%)
Boiler overheated, tripped safety. Usually needs manual reset (small red button). If it trips again, there's an underlying issue.
7. Control board failure (5%)
The "brain" failed. Display blank or nonsensical. Brand-specific replacement, $520-$1,200.
What to do right now if you can't get it working
- Under 32°F overnight forecast: open interior doors, run faucets at a trickle (prevents pipe freeze), call us. We dispatch emergency calls 24/7.
- Above 32°F: schedule same-day or next-morning. Less than emergency rates.
- Document symptoms: error codes, sequence (does it try to start? what sound?), when it last worked. Saves diagnostic time.