Most of this guide applies to hot water boilers, the kind that feed baseboard or radiators through a closed loop. Steam boilers are different, and the notes for them are marked.
Reading the pressure gauge
The gauge on a hot water boiler reads in PSI. On a typical two-story house it sits around 12 to 15 PSI when cold and rises as the water heats. The relief valve opens at 30 PSI.
- Below about 10 PSI cold. The upper floors may not get heat. The system may have a leak or a fill valve problem.
- Climbing toward 30 PSI when hot. Usually a failed expansion tank or a fill valve letting too much water in. Call us.
Steam boilers: check the water level in the sight glass weekly. It should sit roughly halfway. Low water is the most common steam boiler shutdown.
Bleeding radiators
If the top of a radiator or baseboard stays cold while the bottom is warm, there is air in it. With the boiler running, open the bleed valve slowly with a radiator key and a rag underneath. Close it once water comes out steadily. Start on the lowest floor and work up, then check the pressure gauge, since bleeding can drop it. Steam radiators are not bled this way. They have vents that release air on their own.
Noises
- Gurgling in the pipes. Air in the system. Bleeding usually fixes it.
- A rumble or kettle sound from the boiler. Scale on the heat exchanger. Not an emergency, but book a service.
- Banging on a steam system. Often a pipe pitched the wrong way, holding water. Book a visit.