Homeowner Guide· Updated November 2026· Reviewed by ProScore Editorial Team

How to Bleed a Radiator, and Other Ontario Heating-Season Checks

How to bleed a radiator in five minutes, when a hot water tank is due for replacement, who may legally work on gas appliances in Ontario, and where carbon monoxide alarms must go.

To bleed a radiator, turn the heating off and let the radiators cool, hold a cloth under the bleed valve at the top corner, and turn the valve a quarter turn anticlockwise with a radiator key. Air hisses out; close the valve as soon as water appears. Then check the boiler's pressure gauge before you turn the heat back on.

That is the five-minute job. The rest of this guide covers the other two things worth doing before an Ontario winter: deciding whether your hot water tank is due for replacement, and knowing who is allowed to work on anything that burns gas.

How Do I Know a Radiator Needs Bleeding?

A radiator that is warm at the bottom and cold at the top has air trapped in it. Other signs are gurgling or banging when the heat comes on, and rooms that stay cold while the rest of the house is warm.

Natural Resources Canada recommends bleeding radiators once or twice a year so they fill fully with water: a hot-water system works best when its radiators are free of air bubbles and running at the right pressure. Some systems bleed air automatically. If yours has automatic air vents, you may never need to do this by hand.

This guide is for hot-water radiators heated by a boiler. Steam radiators work differently, and their valves are not meant to be opened by hand.

How to Bleed a Radiator, Step by Step

You need a radiator key (a small square key sold at any hardware store) or a flat screwdriver for valves with a slot, an old cloth, and a small container.

1.Turn the heating off and wait until the radiators are cool. Bleeding a hot radiator can spray scalding water.

2.Start on the lowest floor, with the radiator furthest from the boiler, then work up and toward the boiler.

3.Find the bleed valve. It is a small square or slotted fitting at the top corner of the radiator, on the end opposite the main valve.

4.Hold the cloth under the valve and the container below it.

5.Turn the key a quarter turn anticlockwise. You will hear air hiss out. Do not open the valve more than a turn.

6.Close the valve as soon as water appears in a steady drip, not spitting air.

7.Repeat on every radiator, working up through the house.

8.Check the boiler's pressure gauge. Letting air out lowers the pressure. If the needle sits below the range marked on the gauge or the boiler's label, the system needs topping up. Many boilers have a fill valve for this; if you are not sure how yours works, call a heating contractor rather than guessing.

9.Turn the heating back on and check, an hour later, that each radiator is warm from top to bottom.

If a radiator still has a cold top after bleeding, or needs bleeding every few days, air is getting into the system somewhere. That is a job for a heating contractor.

When Should I Replace My Hot Water Tank?

Natural Resources Canada says the single biggest factor in how long a water heater lasts is the quality of the water it heats, and recommends replacing a tank close to the end of its life rather than waiting for it to fail, so you can choose a replacement calmly instead of in an emergency. Its rule of thumb: if your water heater is more than 10 years old, consider replacing it with an ENERGY STAR model.

Signs a tank is near the end:

•Water pooling around the base, or moisture on the tank itself

•Rust-coloured hot water when the cold water runs clear

•Popping or rumbling as the tank heats, which is usually sediment built up inside

•Hot water that runs out sooner than it used to

A leak from the tank itself cannot be repaired. A leak from a fitting or valve often can, so have it checked before you decide.

Do You Rent Your Water Heater?

Many Ontario homes rent their water heater rather than own it. If you do, the rental company is usually responsible for replacing a failed tank, so check your agreement before you buy one. Ontario's rules on home service contracts also matter here:

•No uninvited door-to-door sales. A salesperson cannot sell or rent you a water heater at your door unless you invited them by appointment.

•Ten days to cancel. You can cancel a contract signed at your home within 10 days of receiving your written copy, for any reason. Cancel in writing so you have proof.

•Switching has costs. A new rental usually means ending your existing contract, and there may be fees for ending it and for removing the old tank. Ask your current supplier about an upgrade first.

If a gas tank is being replaced, the installation is gas work, which brings us to the last check.

Who Can Work on Gas Appliances in Ontario?

Only a qualified, registered professional. Under Ontario's fuel safety rules, a person needs a certificate from the Technical Standards and Safety Authority (TSSA) to install, repair, service or remove a gas appliance, and a business doing that work must be a TSSA-registered contractor. TSSA says furnaces and fuel-fired appliances must be maintained by registered contractors who employ certified gas technicians.

That covers a gas furnace, a gas boiler, a gas water heater, a gas fireplace and the gas lines that feed them. It does not cover bleeding a radiator, which is on the water side of the system.

Before you hire, check the business on TSSA's fuels contractor lookup. TSSA warns that unregistered workers often offer discounted rates and use substandard parts, and their work is never audited. For how to read a gas contractor's credentials and reviews side by side, see HVAC contractors on ProScore, and for gas safety at home, read our gas appliance safety guide.

Do I Need a Carbon Monoxide Alarm?

Yes, if your home burns fuel. Under Ontario's Fire Code, a house needs a carbon monoxide alarm if it has a fuel-burning appliance, a fireplace or an attached garage. The alarm goes beside each sleeping area, and since January 1, 2026 on every storey of the home as well, including floors with no bedrooms.

If the alarm sounds, get everyone out of the house first, then call 9-1-1 from outside. Carbon monoxide has no smell, and early symptoms such as headache, nausea and dizziness are easy to mistake for the flu.

The Ontario government also advises having fuel-burning appliances, chimneys and vents cleaned and inspected by a professional every year, before cold weather sets in.

Your Heating-Season Checklist

1.Bleed the radiators if you have a boiler, and check the pressure afterward.

2.Check the water heater's age and look for leaks, rust or rumbling.

3.Book the annual inspection of the furnace, boiler or water heater with a TSSA-registered contractor.

4.Test every carbon monoxide alarm, and add one on any storey that does not have one.

If you are replacing equipment this winter, Ontario's Home Renovation Savings Program pays rebates on heat pumps and heat pump water heaters, and our comparison of heat pumps and gas furnaces covers whether switching makes sense for your home. For plumbing work on the tank itself, compare plumbers across Ontario.

FAQ

How often should I bleed my radiators?

Natural Resources Canada recommends bleeding hot-water radiators once or twice a year, so they fill fully with water and heat evenly. Do it more often if a radiator stays cold at the top.

Do I need to turn the heating off to bleed a radiator?

Yes. Turn the heating off and let the radiators cool first, because water inside a hot radiator can spray out scalding hot when you open the bleed valve.

Can I replace a gas water heater myself in Ontario?

No. Installing or removing a gas appliance in Ontario must be done by a person holding a TSSA certificate, working for a TSSA-registered contractor. Check the contractor on TSSA's online lookup before you hire them.

How long does a hot water tank last?

It depends most on the quality of your water. Natural Resources Canada suggests considering a replacement once a water heater is more than 10 years old, before it fails, so you can choose a new one without an emergency.

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