Boiler Losing Pressure — Diagnosis

On a commercial or institutional closed-loop boiler, pressure is a key indicator: it ensures the loop stays full, that circulation happens and that safety devices can operate. A recurring pressure loss is not trivial — it often reflects a loop imbalance or a component reaching end of life, and can lead to shutdowns, uneven heating or accelerated pump wear.

Where does pressure loss come from?

On a hot water boiler, the common sources are varied: a waterlogged expansion tank (ruptured bladder or lost air cushion), dissolved air venting slowly, a micro-weep at a fitting or joint, a safety relief valve that is venting, or an automatic fill device that no longer holds the setpoint. Some causes are benign and are corrected during maintenance; others, such as a cracked heat exchanger, demand a serious diagnosis. Without proper testing, assigning the cause remotely is risky.

What can you check from the mechanical room?

Note the gauge reading cold and hot, the rate of the drop and how often makeup water runs. Look for water traces under the relief valve, on the piping or at the base of the equipment, and check whether the automatic fill activates often. Do not bleed or adjust pressurized components yourself without procedure and competence: risk of burns, spray and mishandling. If you detect a gas smell, apply your gas safety procedure before anything else.

Why leave the diagnosis to a professional?

Telling a failed expansion tank apart from an early leak or a fill-valve issue requires measurements and method. A preventive maintenance program helps catch a pressure drift before a shutdown, and a qualified intervention avoids repeatedly compensating for a fault that is getting worse. Montréal Combustion diagnoses and corrects pressure problems on commercial boilers across the Greater Montréal, North Shore and South Shore. 450-473-0909.

Frequently Asked Questions

Can I just add water to bring the pressure back up?

Topping up can restore pressure briefly, but it masks the cause and overfilling risks tripping the relief valve. If pressure keeps dropping, it is a symptom to diagnose, not to compensate for repeatedly.

Is low pressure dangerous?

On its own, low pressure mainly degrades circulation and heating and can trigger safety shutdowns. However, a discharging relief valve, repeated pressure loss or any doubt about the heat exchanger warrant a professional's assessment.

Why does pressure drop with no visible leak?

Several causes leave no puddle: a waterlogged expansion tank, dissolved air escaping, a micro-weep at a fitting, a relief valve venting, or a failing automatic fill valve. Only targeted testing can tell them apart.