Troubleshooting
Weak Hot Water Flow From a Combi Boiler
When the hot tap trickles but cold runs fine.
If your hot water flow is noticeably weaker than your cold, the issue is usually on the boiler's hot water side — commonly a scaled plate heat exchanger, a partially blocked filter, or a flow valve problem. Low incoming mains pressure can also limit a combi's output.
Because the fix involves opening the appliance, it's licensed work. A technician can descale or replace the affected part.
Common causes
- Limescale in the plate heat exchanger
- Blocked inlet filter or aerator
- Failing flow valve
- Low incoming mains water pressure
- Partially closed isolation valve
This is not a DIY repair
Combi boilers are gas-fired appliances regulated under the BC Safety Standards Act. Opening the unit, touching the gas valve, or working on the flue without a valid BC gas-fitter licence is both unsafe and illegal. Diagnosing the fault is helpful — fixing it should always be left to a certified technician.
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