Viessmann · Vitodens 100-W combi
74 boiler fault code
Vitodens 100-W type B1KF combi
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What 74 means
System pressure too low (burner locked out; internal circulation pump off; no central heating and no DHW heating)
Safe check
Check the boiler's pressure gauge. If it reads low with the boiler cold, top up the system to the pressure in your user guide (usually 1 to 1.5 bar) using the filling loop, as the user guide describes. If the pressure keeps dropping or the code returns, contact a Gas Safe registered engineer.
When to contact an engineer
The code remains or returns after the step above, or no home step applies; arrange diagnosis by a Gas Safe registered engineer.
Safety notice
A boiler fault code alone is not a gas or carbon-monoxide emergency. If you smell gas, a CO alarm sounds, anyone feels unwell, or there is an unsafe flame, leave and call 0800 111 999 from outside.
Source and provenance
- Viessmann Vitodens 100-W types B1HF/B1KF · chapter 7 “Troubleshooting”, “Fault messages” · code 74, chapter 7 “Troubleshooting”, “Fault messages”, p. 71
installation and service instructions for contractors
6167586 GB · 3/2023
Renting? Report it to your landlord or housing provider first. They are responsible for gas safety and boiler repairs, and the repair should not cost you.
Did this fix it?
After: Repressurise the boiler