Combi Boiler Hot Water Problems — Flow Rate and Temperature Fixes

Published: July 20, 2026 — CANRO Heating & Cooling — Greater Vancouver, BC

Low Flow Rate

If hot water flow is weaker than cold water, the plate heat exchanger may be partially blocked by scale. Descaling restores flow. Another cause: the inlet filter is clogged with debris. Clean the filter. If flow is equally low on both hot and cold, the issue is your home water supply, not the boiler.

Temperature Fluctuations

Fluctuating hot water temperature from a combi boiler is often caused by: the boiler modulating up and down, the flow rate changing (someone turns on another tap), or a faulty thermistor giving incorrect temperature readings. A buffer tank or recirculation loop can stabilize temperature.

Scalding Risk

Combi boilers can deliver water at 60°C+ which can scald in seconds. Install thermostatic mixing valves at taps used by children or elderly. Set the boiler DHW temperature to 50-55°C as a safety measure. Test your tap water temperature if you are concerned about scalding.

Related Services

Safety Reminder

If you smell gas, suspect carbon monoxide or believe there is an immediate danger, leave the property and contact emergency services or the appropriate gas emergency authority. Do not remain inside — exit the building immediately and call for help from outside.