A Bosch boiler that runs but produces no heat is often a thermostat, valve, or flow issue rather than the boiler itself being broken.
Tell us what you need—we’ll call you back fast.
Quick answer
A Bosch gas boiler that is not producing heat, whether it appears to run without warming the home or will not fire at all, is commonly caused by a thermostat or control fault, a closed or stuck zone valve, low system pressure, an ignition or flame-sensing fault, or trapped air in the heating system. Checking the thermostat, pressure gauge, and whether the boiler is actually attempting to fire narrows down the cause before calling for service.
Need a licensed gas fitter for your gas boiler? Call CANRO at (604) 359-1081 — residential natural-gas heating and hot water across Metro Vancouver since 1999.
Homeowners describe 'no heat' for two genuinely different situations: the boiler will not turn on at all, showing no activity when heat is called for, or the boiler runs, the burner fires, but radiators or the heating zones stay cold anyway. These point toward different causes, so identifying which one you are dealing with is the first useful diagnostic step before a technician even arrives.
If the boiler display is completely dark or unresponsive, the cause is more likely electrical, a tripped breaker, a blown fuse, or a control board fault. If the boiler's display is active and it appears to attempt operation but the home still is not warming up, the cause usually sits somewhere between the boiler and the radiators or heating zones themselves.
A thermostat set incorrectly, with a dead battery, or wired incorrectly after an unrelated repair, will simply never send a call for heat, and the boiler has no way to know it should run. Low system pressure below the manufacturer's minimum will prevent many boilers from firing at all as a safety measure, and this is one of the more common and easily checked causes. An ignition fault, where the boiler attempts to fire but cannot establish or sense a flame, will usually show as a lockout indicator on the display rather than silence.
Trapped air in the heating system is one of the most common reasons radiators stay cool near the top while the boiler itself operates normally, and this is often resolved by bleeding the affected radiators. A zone valve that has failed in the closed position, or a circulator pump that has failed or lost power, will stop hot water from reaching part or all of the distribution system even though the boiler is heating water correctly at the source.
In systems with older cast-iron radiators, common in many character Vancouver homes, sludge buildup can restrict flow enough that some radiators barely warm while others work fine, which is a system issue rather than a boiler fault and often points toward the need for a system flush.
| Symptom | Most likely cause | Homeowner-safe check |
|---|---|---|
| Display completely dark | Power supply, breaker, or fuse | Check the breaker panel and any dedicated fuse/switch |
| Display active, boiler locks out | Ignition or flame-sensing fault | Note the fault indicator; do not repeatedly reset |
| Boiler runs, radiators stay cold at top | Trapped air | Bleed the affected radiators |
| Boiler runs, one zone stays cold | Zone valve or circulator issue | None; requires technician diagnosis |
| No call for heat at all | Thermostat fault or setting | Check batteries, settings, and wiring if accessible |
Checking the thermostat, breaker, and system pressure, and bleeding an obviously air-locked radiator, are reasonable homeowner steps. Anything involving the gas valve, ignition components, circulator pump replacement, or zone valve wiring should go to a Technical Safety BC licensed gas fitter, since misdiagnosing a flow or ignition issue can mean running the system in a condition it was not designed for. If the boiler is attempting repeated ignition without success, treat that as a service call rather than something to keep resetting.
Safety note
If you ever smell gas, hear a hissing sound near the unit, or notice soot, a burning smell, or headaches and drowsiness near the appliance, leave the home immediately and call FortisBC at 1-800-663-9911 from a safe location before doing anything else. Any work on gas piping, venting, or combustion components must be carried out by a Technical Safety BC licensed gas fitter.
This usually means the boiler is heating water at the source but something between the boiler and the rooms, trapped air, a stuck zone valve, or a failed circulator pump, is preventing that heat from reaching the radiators or zones.
Yes, most boilers have a minimum pressure safety cutoff, and pressure below that threshold will prevent the unit from firing at all until it is topped back up to the manufacturer's recommended range.
Start with the cold room's radiator, since bleeding radiators that are already fully heating is unnecessary. If bleeding the cold radiator does not help, the cause is more likely a valve or flow restriction than trapped air.
It is the most likely cause, but confirm the breaker and any dedicated switch before assuming a bigger fault, since a simple tripped breaker is a common and easy explanation.
A no-heat situation during cold weather is worth prompt attention, particularly to avoid pipe freeze risk in exterior-wall plumbing runs, so it is reasonable to treat this as a priority service call rather than something to defer for weeks.
Family-run, TSBC-licensed (gas LGA0043870 · boiler LBP0046450), serving Metro Vancouver homes since 1999. Residential, natural gas only.
Call (604) 359-1081 Email info@canroheat.ca“Canro does an amazing job! Super professional and skilled with everything—boilers, furnaces, and AC. Always a pleasure working with them!”
“Five stars for Canro. We needed a replacement of a 30-year-old boiler. A new high-efficiency unit was installed—clean, professional work.”
“I can’t speak highly enough about George, who was recommended for a boiler service call for my parents’ home. George is excellent.”
25+ years keeping Metro Vancouver homes comfortable. Honest advice, upfront pricing, work that lasts.