S.42
FAULT CODE
Vaillant
Domestic Hot Water Priority Active
Low Severity
DIY Check Possible
The boiler is prioritising domestic hot water demand and heating has been temporarily suspended. This is normal behaviour for a combi boiler.
Step-by-Step Fix Guide
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Step 1
No action required — this is normal operation
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Step 2
Heating will resume when DHW demand drops
Gas Safe Reminder
Work on gas appliances must be carried out by a Gas Safe registered engineer. The steps above cover safe checks a homeowner can perform - any internal component replacement requires a qualified professional. If in doubt, always call an engineer.