Boiler losing pressure

A gas boiler in a Greater Vancouver home usually heats a sealed loop of water. The same water circulates through radiators or in-floor tubing day after day, and little is added or drained except during servicing. The loop carries a small positive pressure so air stays out and water reaches every emitter, and a gauge on or near the boiler shows that pressure. The reading moves with temperature: water expands when heated, so the number climbs while the boiler runs and settles back down once the system cools.

When a boiler is losing pressure, the cold reading keeps falling between visits or the system needs regular topping up. A slow drop over several months is a different situation from a drop overnight, and the pace is one of the first clues a technician uses. A single low reading is not a diagnosis; two cold readings taken days apart, plus a note of how often you top up, describe the problem far better.

Let the system sit unused for a few hours, then read the pressure gauge twice over several days and write both numbers down. Most residential boilers are set up to rest near 12 to 15 psi, roughly 80 to 105 kPa, when cold, but the correct figure for your boiler is the one in its own manual; brands and installations differ, so do not copy a neighbour's setting.

Look, without touching anything, for visible water: under the boiler cabinet, around pump and valve joints, at radiator valves, and on the floor near the boiler. Check whether the small discharge tube from the pressure-relief valve is dripping. If the display is showing an alert, write down the exact wording or code and look it up on this site's brand error-code pages. A code is not a diagnosis, but it is information a technician can act on.

The most straightforward cause is a leak somewhere in the loop: a dripping valve or fitting, a corroded radiator connection, or piping that is failing where you cannot see it. BC homes with in-floor loops, slab runs and wall or ceiling piping can hide small leaks for a long time while the fill water slowly replaces what is lost.

Other faults lose water without leaving an obvious puddle. An expansion tank that has lost its air charge cannot absorb the water's expansion, so pressure can climb to the relief-valve setting when the system is hot; if that valve passes, water is discharged and the system reads low once cold. A fill valve that is not doing its job leaves the system low after any loss. In combination boilers an internal leak can let system water escape through the condensate or drain path, which is harder to spot from outside the casing.

One gauge reading rarely explains a pressure drop, but a short written log usually does. Take the reading only when the system is cold, ideally first thing in the morning before the heating has run, and write down the number and the date. Repeat it over several days rather than several hours, and add two more notes each time: how much water you had to add, if any, and whether the gauge rose as usual while the boiler ran and settled back when it stopped. The difference between the cold and running readings is the expansion behaviour, and the pace of the cold drop is the loss.

If the system has an automatic fill valve, note whether the boiler seems to be quietly topping itself up, because a fill side that keeps feeding can hold the gauge up while the loop is still losing water. A log that shows a steady cold reading alongside a top-up every few days, or a relief-valve discharge tube that stays wet, tells a technician that the loss and the overpressure may be the same story. Write down any alert on the display too and look the code up on this site's brand error-code pages, since low-water protection on some controls produces a fault of its own.

Top-up water restores the number on the gauge, but the boiler's own installation manual explains why it is not a neutral act. One manufacturer's manual instructs that all system leaks be eliminated because the continual introduction of fresh makeup water will reduce boiler life: minerals can build up in the heat exchanger, reduce heat transfer, overheat the exchanger and eventually cause it to fail. The same manual notes the system may carry residual substances that affect water chemistry, and calls for the water's pH and chlorine to be verified within an acceptable range. A sealed heating loop is designed to hold the same water for years, with a sealed, pressurized expansion tank absorbing expansion instead of letting the system discharge water and draw fresh water in.

Every top-up breaks that seal a little and adds dissolved air, which is why a slow leak so often travels with radiators that need bleeding. The practical conclusion is simple: a boiler that needs filling more than once or twice in a heating season is telling you there is a loss to find, not a chore to repeat. Technical Safety BC's annual servicing bulletin lists the expansion tank and the water pressure and temperature set points among the items a technician is expected to check, which is exactly where a homeowner's pressure log leads the diagnosis.

Call when topping up has become more than an occasional seasonal habit, when you can see a leak you cannot stop, or when the pressure is dropping over days rather than weeks. A small hidden leak may be wetting framing, drywall or the insulation under a slab, and the cost of drying and repair tends to grow the longer it runs.

If you have found a visible drip, place a container under it, keep electrical items clear of the water, and leave the boiler running only if it is safe to do so. Call ROMA Heating & Cooling at 778-909-5731 during business hours and describe the pace of the drop and your cold readings; that description helps the technician bring the right parts.

A technician starts from a cold reading, brings the system up to the pressure the boiler's manual specifies, and watches how it holds. If the drop resumes, the loop is isolated zone by zone to find a hidden leak, the pressure-relief valve and its discharge path are checked, the fill assembly is tested, and the expansion tank's air charge is verified with a gauge.

Repairs can range from tightening a fitting or replacing a valve to re-charging or replacing the expansion tank and repairing piping. When a leak is inside the boiler's heat exchanger, the honest conversation is repair versus replacement. Gas work in British Columbia is regulated by Technical Safety BC, which issues permits for gas installations and repairs; ROMA's licensed gas contractors carry out this work under the permit system.