Viessmann · Vitodens 100-W combi
981 boiler fault code
Vitodens 100-W type B1KF combi
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What 981 means
Minimum system pressure is too low during DHW heating.
Safe check
Check the pressure gauge. If pressure is low when the boiler is cold, top up to the pressure in the user guide (usually 1–1.5 bar) via the filling loop as described in the user guide. If pressure drops or the fault returns, contact a Gas Safe registered engineer.
When to contact an engineer
If pressure drops or the fault returns, contact 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 981, printed p. 89
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