Most residential hot water boilers run between 12 and 15 PSI when cold and up to about 20–25 PSI when hot. If your gauge reads outside that range, something may need attention.
How to read a boiler pressure gauge
Most boilers have a combination gauge showing pressure (PSI) and temperature. Check it when the boiler is cold, then again after it's been heating for a while. A small rise as water heats is normal.
Low boiler pressure
Below about 12 PSI cold, upper floors and far radiators may not heat. Common causes are a small leak, a recently bled radiator, or a fill valve that isn't keeping up.
High boiler pressure
If pressure climbs near 30 PSI, the relief valve may open and drip. This often points to a waterlogged expansion tank or a fill valve letting in too much water. High pressure is a safety issue — shut the boiler down and call a technician.
Frequently Asked Questions
+What PSI should my boiler be at?
Typically 12–15 PSI cold and no more than about 25 PSI hot for a residential hot water boiler. Your boiler's label lists the exact range.
+Can I add pressure to my boiler myself?
Some systems have a manual fill, but repeated pressure loss means a leak or failing part. Have it checked so the problem doesn't come back.
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