Common problems guide

The most common Viessmann Vitodens 100-W BPJA 25kW P29 problems

The faults most likely to send a Viessmann Vitodens 100-W BPJA 25kW P29 into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
21 documented codes
6 most common
0 DIY-safe checks
6 engineer needed

The 6 most common faults

01
30 High Engineer

Your boiler has stopped because it has lost track of the water temperature reading it uses to run safely, so it has switched itself off until a qualified engineer checks it.

Est. cost
£120-220
Parts
Boiler water temperature sensor (NTC sensor), Sensor wiring harness or plug, Control PCB (only if the sensor and wiring are fine)
Full guide for 30
02
38 High Engineer

Your boiler has stopped working because it cannot read its water temperature sensor properly, so it has shut itself down as a safety precaution and will need a qualified engineer to check it.

Est. cost
£120-250
Parts
Boiler water temperature sensor (NTC), Sensor lead or wiring harness, Burner assembly (if blocked or damaged)
Full guide for 38
03
51 High Engineer

The boiler has detected a faulty temperature sensor that controls the hot water, so it has stopped heating water for taps and showers, though your central heating may still work.

Est. cost
£120-220
Parts
DHW outlet temperature sensor (Viessmann Vitodens type), Sensor cable or plug connector, Main PCB (only if the sensor and wiring test good but the fault remains)
Full guide for 51
04
52 High Engineer

Your boiler has shut itself down as a precaution because it has detected a fault with the sensor that measures the water temperature leaving the boiler, so it isn't able to heat your home or water safely until this is checked.

Est. cost
£150-250
Parts
Flow temperature sensor, Sensor wiring harness, Main PCB (if the sensor circuit is damaged)
Full guide for 52
05
59 High Engineer

Your boiler has stopped heating the hot water from the tap, but your central heating may still work, and a sensor that checks the hot water temperature appears to have a connection problem that a heating engineer can usually fix.

Est. cost
£150-250
Parts
DHW outlet temperature sensor, Sensor plug and wiring harness, Sensor connection cable
Full guide for 59
06
5A High Engineer

Your boiler has shut itself down because one of its water temperature sensors has lost its connection or failed, so it can't safely heat your home or water until it's checked.

Est. cost
£120-250
Parts
Flow temperature sensor (NTC), Sensor wiring lead or harness, Main PCB (control board), in some cases
Full guide for 5A
Parts most often replaced

on the Viessmann Vitodens 100-W BPJA 25kW P29

Boiler water temperature sensor (NTC sensor)Sensor wiring harness or plugControl PCB (only if the sensor and wiring are fine)Boiler water temperature sensor (NTC)Sensor lead or wiring harnessBurner assembly (if blocked or damaged)

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Viessmann shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 21-code list for the Viessmann Vitodens 100-W BPJA 25kW P29

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →