Combi boiler diverter valve stuck in hot water mode in Greater Vancouver

A combi boiler uses a diverter valve to switch between sending heat to your radiators and sending it to your domestic hot water. When that valve sticks in the hot-water position, your taps stay hot but your home gets cold. Here is how to recognize the problem and what can be done about it.

What happens when the diverter sticks on hot water

The diverter valve normally rests so heat flows to the radiators and only switches to hot water when you open a tap. If it sticks in the hot-water position, the boiler keeps prioritizing domestic hot water and never properly heats the central heating circuit, so radiators stay cool even though the thermostat is calling for heat.

The classic symptom is plenty of hot water at the taps but radiators that will not warm up, or warm only weakly. Worn valve components, debris, or a failed diverter motor are typical causes, and they tend to develop gradually before the valve sticks fully.

• Hot water works fine at the taps
• Radiators stay cold or barely warm
• The thermostat calls for heat but the home does not warm
• Often caused by a worn, jammed, or debris-fouled valve

Safe checks and the proper fix

Before assuming the worst, confirm the thermostat is set above room temperature and has fresh batteries, and check that the boiler is set to allow both heating and hot water rather than a summer or hot-water-only setting. These simple settings explain many cold-radiator complaints.

If the settings are correct and hot water still works while heat does not, a stuck diverter valve is likely. The valve is an internal component, so diagnosis and replacement should be done by a licensed technician, who can also check for the debris or sludge that often causes the valve to stick.

• Set the thermostat above room temperature and replace its batteries
• Confirm the boiler is set for both heating and hot water
• Note whether hot water still works while heat does not
• Have a technician inspect or replace the diverter valve

Frequently Asked Questions

Why do I have hot water but no heat?

A common cause is a diverter valve stuck in the hot-water position, so the boiler will not send heat to the radiators. First confirm the thermostat and boiler mode are set correctly, then have a technician check the valve.

Can I free a stuck diverter valve myself?

No. The diverter valve is inside the boiler, so freeing or replacing it is work for a licensed technician. You can only safely check thermostat settings and boiler mode.

What makes a diverter valve stick?

Worn internal parts, a failed valve motor, or debris and sludge from the heating circuit are the usual culprits. A technician can identify which applies.

Could it be the thermostat instead?

It can. A thermostat set too low, dead batteries, or a boiler left on a hot-water-only mode all mimic this. Rule those out first before suspecting the valve.

HeatLand Heating & Cooling is a licensed and insured, TSBC-certified HVAC company serving homeowners across Greater Vancouver. Our technicians diagnose the real fault, explain your options in plain language, and complete the work safely and to code.

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