A boiler that has sat unused since March is not the same machine that shut down in the spring. Seals dry out, valves seize in position, air works its way into the loop, and the circulator pump hasn't turned in five months.
None of that announces itself until you ask the system for heat. Which is why the busiest week of our heating year is the first genuinely cold week of it — a large share of those calls are failures that were sitting there in September, findable, and cheaper to deal with then.
Here's what's worth doing now, what you can check yourself, and where it stops being a homeowner job.
Run it before you need it
The single most useful thing on this list, and it costs nothing.
Pick a mild day, turn the thermostat up until the system fires, and let it run a full cycle. You are not testing whether it makes heat — you are finding out what's wrong while it's still a scheduling problem rather than an emergency.
Watch and listen for:
- Does it fire at all, and how long does it take?
- Any lockout or fault code on the display
- Noises that weren't there in March — banging, kettling, gurgling
- Does every zone or every radiator actually get warm?
- Anything dripping underneath it once it's up to temperature
A boiler that starts fine on a mild September afternoon can still fail at −30°C, but one that struggles in September is telling you something now.
If it makes popping or banging sounds as it heats, that's worth its own read — why a boiler makes popping noises covers what causes it and whether it's urgent.
Check the pressure
Look at the gauge. Cold, most residential systems sit somewhere around 1 to 1.5 bar, and the correct figure for yours is usually printed on the boiler or in the manual — go by that rather than a number off the internet.
Too low and the boiler will lock out rather than run, often on the first properly cold night when it's working hardest. Too high and the pressure relief valve will discharge, which is what that small pipe running to the outside or a drain is for.
Topping up is straightforward on most systems using the filling loop, and it's a reasonable homeowner job. But treat repeated topping up as a symptom, not a chore. A sealed system shouldn't lose water. If yours does, it's going somewhere — a weeping joint, a failed expansion vessel, or a pressure relief valve passing. Our post on why boilers lose pressure walks through finding it.
Bleed the radiators
Air accumulates over a summer of standing still, and it collects at the highest points in the system.
Turn the heat off, let it cool, then bleed each radiator starting with the one furthest from the boiler. You want a steady dribble of water rather than spitting air.
Then check the pressure again and top up if needed — bleeding releases water, and doing several radiators without repressurising is a common way to trigger a low-pressure lockout the same evening.
If a radiator stays cold at the bottom rather than the top, that isn't air and bleeding won't touch it. Why some radiators are cold and others aren't covers what that pattern actually means.
Free up the thermostatic valves
This one catches people every October.
Thermostatic radiator valves seize in whatever position they've been sitting in since spring — usually closed. The dial turns, the radiator stays cold, and it looks like a much bigger fault than it is.
Pull the head off each valve and check the pin underneath moves freely and springs back. If it's stuck down, work it gently until it frees. Doing this in September takes ten minutes across a whole house.
The condensate line — the Calgary one
If you have a high-efficiency condensing boiler, this is the item on the list most likely to strand you, and it's specific to climates like ours.
Condensing boilers produce acidic water as a by-product, which drains away through a plastic condensate pipe. If any part of that pipe runs through an unheated space — a garage, a crawlspace, an uninsulated wall, or outside — it can freeze in a deep cold snap. When it does, the condensate backs up, the boiler detects it, and it shuts down as a safety response.
It is one of the most common reasons a perfectly healthy boiler stops on the coldest night of the year.
What to look at now:
- Trace the pipe. Find where it runs and whether any of it is exposed to cold.
- Check it's insulated where it passes through unheated space, with proper pipe insulation rather than a wrap of something.
- Check the fall. It should run continuously downhill with no sagging section where water can sit.
- Check the termination isn't going to be buried in snow or blocked by ice at the outlet.
If your boiler has shut down on a very cold night before and come back to life after things warmed up, this was very likely the reason. It's worth fixing properly in September rather than thawing a pipe in January.
Look at the vent terminal
Go outside and find where the boiler vents. It's usually a plastic pipe through a sidewall, sometimes two.
Make sure it's clear of shrubs and debris now, and think about where snow accumulates in winter — drifting against a sidewall terminal, or a roofline dumping onto it, will block it. A blocked flue is a safety shutdown at best.
Same check applies to the air intake if yours is a two-pipe system.
Look underneath and around
You are looking for evidence rather than diagnosing anything.
- Rust or staining on the casing or the floor beneath, which indicates a leak somewhere above
- White or greenish crusting on pipework — a sign of a slow weep that's been evaporating
- Damp patches near fittings
- Anything stored against the boiler. Mechanical rooms accumulate boxes over a summer, and clearance around a boiler exists for combustion air and for service access
A small stain that's been there for years still matters. It's a joint that's giving up slowly.
What actually needs a technician
The above is genuinely useful and none of it needs tools you don't have. These do:
Combustion testing. Checking the burner is running at the correct air-fuel ratio needs an analyser. It affects efficiency, safety and the life of the heat exchanger, and there is no visual substitute for the measurement.
The expansion vessel. It has an air charge behind a diaphragm that gradually depletes. A flat vessel is one of the most common causes of pressure swinging and relief valve discharge, and checking it means isolating and testing it properly.
Heat exchanger inspection. On a condensing boiler this is where scale and combustion deposits accumulate, and Calgary's hard water is unkind to them.
Cleaning the condensate trap. It gets a sludge of acidic residue that eventually blocks it — same shutdown as a frozen line, different cause.
Safety controls. Pressure relief valve, limit controls, the low water cutoff if fitted. These exist to prevent the worst outcomes and are worth confirming actually function.
That's what an annual boiler service covers, and it's the reason we push for September and October appointments rather than fitting them around emergencies in January.
If it's an old system
Some honesty is useful here. If your boiler is well into its second decade, has needed repairs in each of the last couple of seasons, and the parts are getting harder to source, a service is maintenance on a decision you're going to face soon anyway.
That isn't a reason to replace it this year. It is a reason to know where you stand before winter rather than during it — how long boilers last in Calgary covers the realistic lifespan and what shortens it here.
What we'd rather not do is meet you for the first time at −30°C with a failed heat exchanger and no heat in the house, because at that point every option is a bad one.
The short version
Run it now. Check the pressure. Bleed the radiators and repressurise. Free the valves. Trace the condensate line and insulate anything exposed. Clear the vent. Look underneath for stains.
Then book the service while there's still a choice of dates.
If anything on this list turned up something, or you'd rather have it looked at properly before the season starts, call 587-834-3668. See boiler repair if something has already failed, or boiler replacement if you're weighing whether this is the last winter for it.
