Boiler shows E25, CH flow temperature rises too quickly at low load

Safety: Surfaces may be hot. Allow system to cool before adjusting valves.

User checks:

• Ensure at least a few radiators have their thermostatic radiator valves (TRVs) fully open.
• Check that any manual bypass radiator (usually in the hall or bathroom) is open.

Engineer checks:

• Verify that a suitable automatic bypass valve is installed and correctly set for the Keston boiler.
• Check and clean any system filter or strainer on the return pipework.
• Increase pump speed if set too low, ensuring noise and flow remain acceptable.
• Advise on correct TRV usage to maintain minimum flow through the boiler.