On a Buderus combi-style wall-hung boiler, losing hot water at the taps while the heating system keeps running, or the reverse, usually points to a stuck or worn diverter valve.
Tell us what you need—we’ll call you back fast.
Quick answer
A diverter valve on a Buderus combi boiler switches priority between domestic hot water and space heating so that a tap being turned on gets a fast hot-water response rather than waiting behind a heating call. When the valve sticks, wears, or its actuator motor fails, homeowners typically notice either no hot water while heating still runs, lukewarm mixed water, or radiators that stay warm even when only a tap is calling for hot water.
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.
A combi boiler heats both domestic hot water and space heating from a single heat exchanger, and the diverter valve is what decides, moment to moment, which one gets priority. When a hot water tap opens, the valve is supposed to shift flow to prioritize domestic hot water for a fast, strong response, then shift back to heating once the tap closes.
This is different from a system with a separate indirect tank, where priority is usually handled by a simpler zone valve rather than a dedicated diverter integrated into the boiler body itself.
The most common complaint is losing hot water at the tap specifically while the heating system is also running, or the opposite: radiators staying warm even though only a hot water tap is open. A valve stuck partway between positions can produce lukewarm water at the tap because flow is being split rather than fully diverted.
A technician checks the diverter valve's actuator motor for power and proper travel, since a motor that's receiving power but not moving the valve fully is a common failure mode. The valve body itself is inspected for mineral buildup or debris jamming it partway open.
Metro Vancouver's municipal water is comparatively soft, which reduces scale buildup compared with Fraser Valley well water, but older piping and fittings can still shed debris that lodges in a valve over years, so it's checked regardless of water source. If the boiler has a valve position sensor, that's checked as well to confirm the control board is getting accurate feedback.
The relevant section of the boiler's internal plumbing is drained down, the actuator is unbolted from the valve body, and either the actuator alone or the full valve assembly is replaced depending on which component has failed. After reassembly, the system is refilled and bled, and the technician runs both a heating call and a hot water call to confirm the valve correctly prioritizes each.
Because the diverter is internal to the boiler body on most wall-hung combi units, this job is usually completed within the mechanical room without disturbing the rest of the heating distribution piping.
Diverter valve wear is common on combi boilers with heavy domestic hot water cycling, such as households with multiple bathrooms or a secondary suite, and replacing the valve or actuator is a routine, contained repair on an otherwise healthy boiler.
If the valve failure comes alongside other unrelated issues on an older unit, it's a reasonable point to ask your technician for a broader assessment before committing to the repair.
Safety note
If a gas boiler or gas water heater ever smells like gas, is sooting, or is tripping repeatedly on a safety lockout, treat it as a safety issue rather than a project to finish yourself: leave the home, do not operate switches or open flames, and call FortisBC at 1-800-663-9911 from outside. Gas valve, burner, and combustion work in BC must be performed by a Technical Safety BC licensed gas fitter.
This usually means the diverter valve isn't fully shifting priority to domestic hot water when a tap opens, often due to a worn valve body or a weak actuator motor.
They serve a similar purpose but aren't identical. A diverter valve is typically built into a combi boiler to split flow between heating and domestic hot water, while a zone valve is more commonly used with a separate indirect hot water tank.
A diverter valve stuck partway between positions can split flow between the heating and hot water sides at once, producing a mixed, lukewarm result at the tap rather than a clean switch.
Yes, households with multiple bathrooms or a secondary suite cycle the valve more frequently as hot water and heating calls overlap, which can accelerate wear compared with a lighter-use household.
You can observe the symptoms, like hot water dropping out during a heating call, but diagnosing and accessing the valve itself involves working inside the boiler's internal plumbing, which should be left to a licensed technician.
Not necessarily. Low pressure at a specific tap is more often a fixture, aerator, or supply-line issue, while a diverter valve problem specifically shows up as heating and hot water competing rather than pressure loss alone. Your technician can tell them apart.
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.