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When your combi boiler heats the house fine but won’t produce hot water (or produces lukewarm water), the problem is almost always in the DHW circuit — separate from the heating circuit. Here are the most common causes.
The DHW plate HX scales rapidly with Vancouver hard water — annual descaling is essential. Severe scaling reduces flow and hot-water output dramatically.
Symptom: Hot water flows slowly, never gets very hot, takes ages to warm up.
Fix: Descale (CANRO service, $150-$250) or replace plate HX if severely damaged.
The boiler won’t fire for DHW unless it detects flow (typically >0.5 GPM). A failed flow sensor doesn’t trigger DHW mode.
Symptom: Heating works fine, opening a hot tap produces cold water.
Fix: Flow sensor cleaning or replacement (~$300-$450).
The internal three-way valve diverts boiler output between heating and DHW. If stuck in heating position, DHW gets no priority — cold water continues.
Symptom: Heating works, no hot water at all (not even lukewarm).
Fix: Valve cleaning or replacement (~$450-$850).
Easy DIY check. The DHW set point on the boiler should be 49-55°C (120-130°F). If someone changed it to a lower value, hot water won’t feel hot.
Fix: Increase DHW set point on the front panel.
Some Vancouver homes have anti-scald mixing valves at individual fixtures. If the valve is failing, it lets too much cold water mix in.
Symptom: One fixture is lukewarm, others are fine.
Fix: Replace the mixing valve at the fixture (plumber, not HVAC).
Some boiler error codes shut down DHW while keeping heating functional, or vice versa. Note the code and check our brand-specific error code guides.
Same-day diagnostic. Most DHW issues resolved on first visit because plate HX, flow sensors, and diverter valves are in every truck.
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If you are considering combi boilers, this guide walks through the key technical and practical points specific to Metro Vancouver. A combi (combination) boiler provides both space heating AND on-demand domestic hot water from a single wall-hung unit, eliminating the separate hot-water tank. Modern combi units in Metro Vancouver run at 95-98% AFUE with modulating burners.
Metro Vancouver's housing stock ranges from early-1900s character homes with hydronic radiator systems to modern condos with combi boilers — equipment selection and serviceability vary dramatically by housing era. CANRO has worked with combi boiler systems across Metro Vancouver since 1999, including installations and service calls in Capilano, Sullivan, Edgemont and Brighouse.
Sizing. Combi sizing balances heating load (Manual J) against DHW peak demand (gallons per minute at design temperature rise). Vancouver's 7-9°C incoming water needs ~32°C rise for typical use — usually requiring 150,000+ BTU input.
Lifespan. A combi boiler typically lasts 12-18 years in Vancouver. The DHW side is the limiting factor — annual descaling and combustion service extends life significantly.
Warning signs. Combi-boiler issues include flow-rate drops (scale build-up in the secondary heat exchanger), domestic-hot-water temperature swings, ignition lockouts, and condensate-trap obstructions.
Combi sizing balances two loads: heat-loss calculation (Manual J) for space heating, and peak DHW demand (gallons per minute at design temperature rise). Vancouver's 7-9°C incoming water needs ~32°C rise — typical family installs need 150,000-200,000 BTU input.
A combi boiler heats BOTH the hydronic heating loop AND domestic hot water; a tankless water heater handles ONLY domestic hot water. Combi units use the same heat exchanger for both via internal valving — efficient and space-saving, but slightly more complex than a dedicated tankless plus separate heating boiler.
Top combi options for Vancouver homes: Navien NCB-H (best turn-down ratio, built-in recirculation option), IBC SL series (BC-engineered, local technical support), Viessmann Vitodens 222-F (premium European engineering), and Baxi Luna Duo-tec (compact wall-hung). All are properly stocked locally for parts.
A properly sized combi delivers continuous DHW that beats any tank for long showers, but peak simultaneous flow may be slightly lower than a tank for very brief peaks (e.g. two showers + dishwasher all starting at once). Modulating combis with high turn-down ratios (1:10 or better) handle this well.
Annual servicing is essential for combi boilers. The DHW side requires descaling in Metro Vancouver's moderately hard water; the heating side needs combustion analysis, expansion tank check, and condensate-trap cleaning. Skipping service significantly shortens lifespan and voids most manufacturer warranties.
Combi boilers work well for 1-3 bathroom homes where you want to free up the floor space currently taken by a hot-water tank. For 4+ bathroom homes or homes with significant simultaneous DHW demand (multiple showers + dishwasher + laundry), a heating-only boiler plus an indirect tank usually delivers better DHW performance.
To book combi boiler service or get a free written quote for installation, call CANRO at (604) 359-1081 or email info@canroheat.ca. We service all of Metro Vancouver including Capilano, Sullivan, Edgemont and Brighouse.
This guide was written by the CANRO Heating & Cooling team based on 25+ years of combi boiler installation, repair and annual service work across Metro Vancouver. Last reviewed May 2026.
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