Viessmann 50 Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann 50 fault code mean?
Fault code 50 on Viessmann boilers — most commonly seen on the Vitodens 200-W and 222-F — signals that domestic hot water (DHW) production has been suspended because the boiler has detected a short circuit on the DHW tank temperature sensor (NTC). In plain terms, the control unit cannot get a reliable temperature reading from the hot water circuit, so it shuts down DHW as a precaution. Your central heating should continue to work normally, but taps and showers will run cold. Codes 51, 58, and 59 sit in the same DHW sensor/fault family: code 51 typically indicates an open circuit (broken signal) rather than a short, while 58 and 59 relate to further DHW sensor or circuit deviations — if you see any of these alongside or instead of 50, the same diagnostic approach applies.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Short-circuited DHW NTC temperature sensor Common
The most direct cause of code 50: the NTC sensor measuring the domestic hot water temperature has internally short-circuited, sending an out-of-range resistance signal to the control board. The boiler interprets this as a sensor failure and halts DHW heating.
- Damaged or chafed sensor wiring Common
The cable run between the DHW sensor and the boiler's control unit can become pinched, chafed, or develop a short where two conductors touch. Even a small amount of moisture ingress into a connector can mimic a sensor short circuit and trigger code 50.
- Loose or corroded wiring connector Sometimes
Vibration over time can loosen the plug-in connector at the sensor end or at the PCB terminal. Corrosion on the pins increases resistance or causes intermittent short circuits, producing an erratic or invalid sensor reading.
- Limescale build-up on the sensor probe Sometimes
In hard-water areas, scale can accumulate around the sensor probe and insulate it from the water it is meant to measure. While this more typically causes slow or inaccurate readings, heavy scaling can stress the sensor element and contribute to failure.
- Faulty PCB (control board) Rare
If the sensor and all its wiring test within specification, the fault can originate on the PCB itself — specifically the sensor input circuit. PCB faults are relatively uncommon but should be considered once all other components have been ruled out.
How to fix it
- Check that your hot water is genuinely not working DIY safe
Run a hot tap for 30–60 seconds to confirm there is no hot water. Check that your heating radiators are still warming up — code 50 typically affects DHW only, so if heating has also stopped, there may be an additional fault present.
- Reset the boiler once DIY safe
Locate the reset button on your Viessmann boiler (usually a flame symbol button or a menu-based reset depending on the model). Hold it for the specified time per your user manual. If the boiler restarts and hot water returns, monitor it over the next few hours. If code 50 returns, do not keep resetting — repeated resets will not fix a failed sensor and may mask a worsening fault.
- Check your boiler's system pressure DIY safe
Glance at the pressure gauge on the boiler — it should read between 1.0 and 1.5 bar when cold. If it has dropped below 0.8 bar, top it up via the filling loop following your user manual. Low pressure alone won't cause code 50, but it is worth ruling out before calling an engineer.
- Arrange a Gas Safe registered engineer to inspect the DHW sensor and wiring Gas Safe engineer
The engineer will disconnect and electrically test the DHW NTC sensor, measuring its resistance against the manufacturer's temperature-resistance curve. They will also inspect the full cable run from the sensor to the PCB, looking for chafing, pinching, moisture ingress, or corroded connectors. This is not a job for an unqualified person — the sensor is an electrical component within the boiler's sealed control system.
- Have the engineer replace the DHW temperature sensor if it is found to be faulty Gas Safe engineer
If the sensor reads outside specification or has a confirmed short circuit, a like-for-like replacement NTC sensor will be fitted and the boiler retested. On Vitodens models the sensor is a straightforward component swap for a qualified engineer, and hot water should be restored the same day.
- Have the engineer inspect and clean or descale the sensor pocket Gas Safe engineer
In hard-water areas, the engineer may find scale build-up in the sensor pocket or around the probe. Descaling or replacing the sensor assembly addresses this and helps prevent a premature repeat failure. If your area has notably hard water, discuss a scale reducer or inhibitor top-up at the same visit.
- Have the engineer check the PCB if sensor and wiring are within specification Gas Safe engineer
If all sensor readings and wiring connections are good but code 50 persists, the PCB sensor-input circuit is the next suspect. PCB diagnosis and replacement is a specialist task — costs are higher, so a reputable engineer will confirm this diagnosis before proceeding. Check whether your boiler is still within its Viessmann warranty (up to 10–12 years on Vitodens models) as a PCB replacement under warranty costs you nothing.
Parts you may need
- DHW NTC temperature sensor (Vitodens 200-W / 222-F compatible) · from £35
- Sensor wiring loom / connector repair kit · from £20
- PCB (control unit) — Vitodens 200-W · from £320
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £120–£320, depending on the underlying cause.
Frequently asked questions
Can I still use my heating while fault code 50 is showing?
Yes — in most cases, code 50 only disables domestic hot water production while leaving the central heating circuit unaffected. Your radiators should continue to work normally. That said, do not ignore the fault; a failed sensor left unaddressed can occasionally lead to broader control issues.
Will resetting the boiler clear fault code 50 permanently?
A reset may temporarily clear the code, but if the DHW temperature sensor has genuinely short-circuited, the fault will return — often within minutes or hours. One reset is worth trying, but if code 50 comes back, stop resetting and call a Gas Safe engineer. Repeated resets will not repair a failed sensor.
How much does it cost to fix Viessmann fault code 50 in the UK?
For most homeowners, the repair involves the engineer's call-out, diagnosis, and a DHW NTC sensor replacement, coming to roughly £120–£320 in total including parts and labour. If the PCB is found to be faulty instead, costs can rise to £500 or more — but this is uncommon. Always check whether your Viessmann boiler is still within its manufacturer warranty (Vitodens models can carry up to 10–12 years of cover), as sensor and PCB replacements may be free if carried out by an approved technician.
What is the difference between Viessmann fault codes 50, 51, 58, and 59?
All four codes sit in the same DHW sensor fault family. Code 50 specifically indicates a short circuit on the DHW tank temperature sensor — the sensor's resistance has dropped to near zero. Code 51 is the opposite problem: an open circuit, meaning the sensor signal is completely absent (broken wire or failed sensor element). Codes 58 and 59 relate to further deviations or faults within the DHW sensor circuit. In practice, the diagnostic and repair approach is very similar for all four: a Gas Safe engineer will test the sensor and wiring and replace whichever component is out of specification.