What belongs on a boiler maintenance checklist?
Updated August 2026
A boiler's checklist is short but strict: one $150–300 pro service each fall, cold pressure held near 12 to 15 psi, a yearly radiator bleed, and a pressure-relief-valve test. Low water and a stuck relief valve are the two conditions that turn a heating appliance into a safety problem, so they lead the list. Handled every year, a boiler is one of the longest-lived systems in the house, often 15 to 30 years.
| Task | Interval | Effort |
|---|---|---|
| Read the pressure gauge, aim 12–15 psi cold | Monthly | 2 min · DIY |
| Look and listen for leaks or drips at fittings | Monthly | 3 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Bleed trapped air from each radiator | Yearly | 30 min · DIY |
| Test the pressure-relief valve | Yearly | 5 min · DIY |
| Check the expansion tank and low-water cutoff | Yearly | 10 min · DIY |
| Task | Interval | Effort |
|---|---|---|
| Combustion, venting, and heat-exchanger check | Yearly | $150–300 pro |
| Flush or dose the system to clear sludge | As needed | incl. or +$100 |
What neglect costs
Air trapped in the system leaves radiators cold at the top and the boiler short-cycling, which is why the yearly bleed matters. Let pressure run too low and the boiler locks out or overheats; too high and the relief valve dumps water. Sludge and corrosion inside an unflushed system clog the heat exchanger, and a replacement exchanger runs $500–1,500. The worst case is a failed low-water cutoff or stuck relief valve, a genuine rupture risk, which is exactly what the $150–300 annual service is there to catch.
Leave these to a pro
The annual service ($150–300, best booked in early fall) covers the combustion and flue check, the heat exchanger, and the safety controls, the low-water cutoff and relief valve, that you should never assume are working. A system flush or inhibitor dose to clear sludge is a good add-on every few years. You can bleed radiators, read the pressure gauge, and top up the feed yourself; the gas, venting, and safety devices belong to a qualified heating engineer.
This whole checklist ships as reminders in OnOtto: every task above, on the right schedule for your home, snooze-proof.
Load this checklist as remindersFrequently asked questions
What pressure should my boiler be at?
Most residential boilers sit around 12 to 15 psi when cold and rise a few psi as the water heats, staying under about 25 psi. If the cold reading keeps dropping, you have a leak or a failing expansion tank; if it climbs toward the relief valve's 30 psi cutoff, the expansion tank or fill valve needs attention. Use the manual fill valve to top a low system back to 12 psi, slowly.
How do I bleed my radiators?
With the system warm then shut off, hold a cloth under the bleed valve at the top of each radiator and turn the key a quarter-turn until air hisses out, then close it the moment water dribbles. Start with the lowest radiators and work up, or hit the upstairs ones first if that is where the cold spots are. Recheck boiler pressure afterward and top it back to 12 to 15 psi, since bleeding drops it.
Why is my boiler losing pressure?
A steady drop almost always means water is escaping: a small leak at a radiator valve or pipe joint, a weeping pressure-relief valve, or a waterlogged expansion tank that no longer cushions the system. Check for damp patches around fittings and under radiators first. Topping it up over and over just masks the leak, so trace the source. A persistent drop with no visible leak is a service call.
How long does a boiler last?
Cast-iron boilers commonly run 20 to 30 years, and modern high-efficiency condensing units 15 to 20, with annual service being the biggest factor in reaching either. Signs it is near the end include rising bills, frequent repairs, visible corrosion or leaks at the block, and kettling noises. Past 15 years with a major part failing, price a replacement against the repair before committing.