BoilerFaultCodesWhat the manual says
Manufacturer manualBoiler is in waiting period of modulation block/operation block function due to water shortage (flow-return spread too large)
From this model's manual
Verified against the Vaillant/Vaillant Ecotec Plus 937 07 2012 Isim installation & service manual.
DIY fix possible
Check that all your radiator valves are fully open to allow good water flow.Check your boiler pressure gauge to ensure it sits between 1 and 1.5 bar, and top it up using the filling loop if it is too low.Bleed your radiators to release any trapped air that might be blocking the water circulation.
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Related fault codes
All 72 fault codes on the ecoTEC plus 937 VUI GB 376/5-5
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