Boiler Won’t Shut Off, Leaking, or Making Noise? Common Problems Explained
First, Is This an Emergency?
Stop and call if:
- You smell gas (rotten eggs or sulphur). Leave right away. Don’t switch lights or appliances on or off, use your phone inside, smoke, or start a vehicle. From outside, call the Enbridge Gas 24-hour emergency line at 1-866-763-5427 or 911, then call us. A CO alarm won’t detect a natural gas leak. (Enbridge Gas)
- Your CO alarm sounds, or anyone has headaches, nausea, dizziness, or drowsiness. Get everyone out and call 911 from outside. (Government of Ontario)
- The relief valve is spraying, or the gauge is in the red. Keep clear of the valve.
- It won’t shut off and pipes or radiators are too hot to touch.
- Water is pooling near wiring or an outlet. Don’t stand in it.
- You see soot, scorch marks, or a yellow or orange flame instead of blue.
For the last four, with no gas smell, turn off the boiler’s service switch or breaker (from a dry spot) and call.
Ontario requires CO alarms next to each sleeping area in homes with fuel-burning appliances, and since January 1, 2026, on every storey. Test them monthly. More on carbon monoxide safety.
Why Is My Boiler Still Running When the Thermostat Is Off?
Usually the heat call isn’t ending (a thermostat or wiring issue), or a part at the boiler is stuck on.
Thermostat or Wiring Problems
Check the batteries, heat mode, and any “hold” setting. A shorted thermostat wire also keeps calling for heat. See other signs of a faulty thermostat.
A Stuck Zone Valve, Relay, or Aquastat
A zone valve is the gate that lets hot water into one area of your home. If it sticks open, or a relay (the switch that tells the boiler to run) sticks closed, the boiler keeps firing. So can the aquastat, the boiler’s water temperature control.
When “Always On” Is Actually Normal
Boilers that heat household water through an indirect tank fire in summer for showers. The circulator pump (which moves the hot water) may also run briefly after the burner stops. The tell: hot radiators with the heat off aren’t normal.
Safe check: Set the thermostat 5 degrees below room temperature and wait 10 minutes. Pipes too hot to touch, or the gauge still climbing? Switch the boiler off at its service switch (no gas smell only) and call.
Why Is My Boiler Leaking Water?
A small drip is rarely an emergency, but it’s never normal. Water, electricity, and gas don’t mix.
Leaking From the Bottom
A boiler leaking from the bottom usually means a worn pump seal, a leaky drain valve, or a loose fitting. In older boilers, it can be a corroded or cracked heat exchanger (where the flame heats the water). That’s the expensive one. Note where it collects and whether it’s warm.
Water From the Pressure Relief Valve
A dripping relief valve means pressure is too high, often from a failed expansion tank (which absorbs expanding hot water) or an overfilling fill valve. Never cap, plug, or tighten a relief valve.
Condensate From a High-Efficiency Boiler
Condensing boilers make acidic water (condensate) by design. If its drain line clogs, it pools. Less urgent, still a technician job.
Safe check: Towel it up, snap a photo, and read the gauge. Then book a boiler repair in St. Catharines with Mr. Furnace.
Why Is My Boiler Making Noise?
Most boiler noises mean scale, air, or a wearing part.
Banging or Kettling
Kettling sounds like a kettle about to boil, and banging often comes with it. Minerals in the water leave scale on the heat exchanger, and water trapped underneath flashes to steam. Weak pump flow does the same.
Gurgling or Whistling
Gurgling or whistling usually means trapped air. With the boiler off and cool, open each radiator’s bleed valve with a radiator key until water replaces the hiss. Then recheck the pressure. Not comfortable? Call us.
Noises When the Boiler Isn’t Running
Noise at night, or when it’s not in use? Ticking or creaking as pipes cool is usually normal. Humming or buzzing from a pump or relay isn’t.
Other Common Boiler Problems
- No heat or no hot water. Check the thermostat, breaker, and service switch. Still nothing? Call.
- Boiler keeps shutting off. Short cycling or a safety lockout, meaning it’s protecting itself.
- Pilot light won’t stay lit. Often a thermocouple or flame sensor. Don’t keep relighting it.
- Cold radiators. Cold at the top means air, so bleed them. Cold at the bottom usually means sludge, a technician job.
- Low or dropping pressure. Usually a leak somewhere. Topping up won’t fix that. Call.
Boiler 15+ years old and on its third repair this season? It may be time to weigh repair against boiler replacement and installation.
BOOK A FREE IN HOME ASSESSMENT TO SEE IF A BOILER REPLACEMENT IS RIGHT FOR YOU
What’s Safe to Check Yourself vs. When to Call
Thermostats, breakers, the gauge, and bleeding radiators: fair game. The gas valve, burner, heat exchanger, relief valve, and wiring are not. Under Ontario law, fuel-fired appliances must be maintained by TSSA-registered contractors using certified gas technicians.
| Symptom | Safe to check yourself | Call a technician if… |
|---|---|---|
| Won’t shut off | Thermostat settings and batteries | Radiators stay hot or the gauge climbs |
| Leaking | Where water collects, the gauge | It’s near wiring or from the relief valve |
| Banging or kettling | That radiator valves are open | The noise continues |
| Gurgling | Bleed radiators (boiler off, cool) | It returns or pressure drops |
| Keeps shutting off | Breaker and service switch | It shuts down again |
Also, never drain a hot boiler.
24/7 Boiler Repair in St. Catharines and Across Niagara
Your boiler picked a bad time. We didn’t. The Mr. Furnace team has kept Niagara homes warm since 1978, and we answer 24/7. Same rate at 2 AM as 2 PM, with a clear quote before any work starts. See for yourself why homeowners in Niagara are choosing Mr. Furnace.
We serve St. Catharines, Niagara Falls, Welland, Grimsby, Fort Erie, and Thorold. Call (905) 346-3507 or book a boiler repair online.
Frequently Asked Questions About Boiler Problems
Is a leaking boiler dangerous?
Not usually right away, but leaks grow, and water near electrical parts is risky. Near wiring or from the relief valve? Switch it off (no gas smell only) and call us.
What should my boiler pressure be?
The maximum is stamped on your boiler’s rating plate. Normal pressure sits well below it and varies by system. Ask your technician to note your normal range.
Why does my boiler run in the summer?
That’s normal if it heats your household water through an indirect tank. Hot radiators with the heat off aren’t.
Can I fix my boiler myself?
Anything superficial can be tinkered with but because a boiler involves gas, the rest needs a TSSA-certified gas technician. You should have a professional inspect and maintain your boiler every year before cold weather.