Boiler produces no domestic hot water on a combi model, but space heating works

Safety first: Turn off power and close domestic water isolation valves before servicing DHW components.

• Check for DHW demand recognition: When a hot tap is opened, the boiler should indicate DHW demand on the display. If not, suspect the DHW flow sensor.
• Inspect DHW flow sensor: Remove and clean or replace the sensor as needed.
• Check diverter valve operation: On some Ruud combi models, a motorized diverter valve directs heat to DHW or heating. Listen for valve movement when switching between heating and DHW. A stuck valve may need replacement.
• Descale plate heat exchanger: If the boiler fires but water is only lukewarm, the DHW plate heat exchanger may be scaled and require professional descaling or replacement.