Furnace is running but there is no domestic hot water at taps

Safety first: Hot water circuits can be under mains pressure. Isolate water and power before disassembly.

• Check DHW demand: Open a hot tap fully and observe the furnace display for a DHW demand symbol. If none appears, suspect the DHW flow sensor.
• Clean or replace DHW flow sensor: Remove and inspect the sensor for debris or limescale. Clean or replace as needed.
• Check diverter valve: On combi models, ensure the diverter valve moves to DHW position when a tap is opened. A technician may need to replace the valve motor or cartridge if stuck.
• Descale plate heat exchanger: If the furnace fires but water remains lukewarm, the plate heat exchanger may be scaled and require descaling or replacement.