Viessmann 58 Fault Code: Causes, Fixes & Repair Costs
What does the Viessmann 58 fault code mean?
Fault code 58 on a Viessmann boiler indicates that the control unit has detected an open-circuit or complete loss of signal from the domestic hot water (DHW) temperature sensor. In practical terms, the boiler's electronics can no longer read a valid temperature from the DHW circuit, so as a precaution the boiler stops producing hot water — though space heating typically continues to work normally. The fault points specifically to an interruption (open circuit) in the sensor circuit, distinguishing it from related codes: code 50 signals a short circuit on the DHW cylinder sensor, code 51 a short circuit on a related sensor, and code 59 an interruption on the ACM outlet sensor. If your display shows 58, the open-circuit fault is specifically on the DHW temperature sensor itself or its wiring. Codes 50, 51, 58, and 59 are among the more frequently seen Viessmann error codes and all share the same headline symptom — no hot water but central heating still operating.
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
- Faulty or failed DHW temperature sensor Common
The sensor itself may have reached end of life or suffered an internal break, causing it to present an open circuit to the control board. This is the single most common root cause when code 58 appears without any obvious wiring damage.
- Broken, disconnected, or damaged sensor wiring Common
The cable running from the DHW sensor to the control board can develop an open circuit through vibration, heat fatigue, or physical damage. Even a single broken strand in the cable can be enough to trigger the fault.
- Corroded or loose sensor connector Sometimes
Moisture ingress over time can corrode the plug-in connector at the sensor end or at the board, increasing resistance until the circuit effectively reads as open. A loose connector that has vibrated free will produce the same result.
- PCB (control board) fault Rare
If the wiring and sensor both test correctly, the control board itself may have lost the ability to read the sensor input channel. PCB faults are less common but should be considered after the sensor circuit has been ruled out.
How to fix it
- Check that hot water is genuinely not working and that heating still functions DIY safe
Run a hot tap fully for at least 60 seconds and note whether any warm water is produced. Also check that radiators are heating normally. Confirming the pattern — no DHW but heating present — helps verify a DHW-specific sensor fault rather than a total boiler failure, and is useful information to pass on to your engineer.
- Reset the boiler once or twice following Viessmann's procedure DIY safe
Press and hold the reset button for approximately ten seconds, then wait two to three minutes for the boiler to attempt a restart. If code 58 clears and hot water is restored, monitor the boiler over the next day or two. If the code returns promptly, a reset is not a lasting fix — the underlying sensor fault must be investigated. Do not repeatedly reset more than two or three times in total.
- Engineer to inspect the DHW sensor wiring and connectors Gas Safe engineer
A Gas Safe registered engineer will trace the sensor cable from the DHW cylinder or heat exchanger back to the control board, checking for breaks, pinched sections, or signs of heat damage. Connectors at both ends will be reseated or replaced if corrosion or looseness is found. This is often all that is needed if the sensor itself is intact.
- Engineer to test the sensor resistance with a multimeter Gas Safe engineer
Using a multimeter set to resistance (ohms), the engineer measures across the sensor terminals. An open-circuit reading (infinite or overrange resistance) confirms the sensor has failed internally. A reading within the manufacturer's specified range for the current temperature indicates the sensor is sound and the fault lies in the wiring or board.
- Engineer to replace the DHW temperature sensor if found faulty Gas Safe engineer
DHW temperature sensors are model-specific components. The engineer will source the correct part — either directly from Viessmann or a reputable heating parts supplier — and fit it. The system will then be tested to confirm code 58 has cleared and hot water is restored.
- Engineer to investigate the PCB if sensor and wiring are sound Gas Safe engineer
If the sensor resistance is correct and the wiring is undamaged, the control board's input circuit may be at fault. PCB diagnosis and replacement requires specialist knowledge. Note that PCB faults on Viessmann boilers within the warranty period may be covered at no cost — check with Viessmann UK on 01952 675000 before authorising out-of-warranty repair work.
- Book a Gas Safe registered engineer if the fault persists after resetting Gas Safe engineer
Code 58 is not a fault a homeowner can resolve internally. If resetting the boiler does not clear the code, or if it returns within a short time, contact a Gas Safe registered engineer — ideally one with Viessmann experience — to carry out the full diagnostic process above.
Parts you may need
- Viessmann DHW temperature sensor (NTC) · from £35
- Sensor connector/wiring harness · from £20
- Viessmann control board (PCB) · from £380
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 £100–£200, depending on the underlying cause.
Frequently asked questions
Why does my Viessmann boiler show fault 58 but the heating still works?
Code 58 is specific to the domestic hot water sensor circuit — it does not affect the central heating sensor, which is on a separate circuit. That is why your radiators continue to work normally while hot water production stops. Once the DHW sensor or its wiring is repaired, full hot water should be restored without any impact on your heating.
What is the difference between Viessmann codes 50, 51, 58, and 59?
All four codes relate to the DHW temperature sensing circuit and share the same main symptom — no hot water. Code 50 is a short circuit on the DHW cylinder sensor; code 51 is a short circuit on a related sensor; code 58 is an open circuit (interruption) on the DHW sensor; and code 59 is an open circuit on the ACM outlet sensor. The distinction matters because a short circuit and an open circuit point to different failure modes, even though the fix is often similar — sensor or wiring replacement by a Gas Safe engineer.
Can I fix Viessmann fault code 58 myself?
The safe homeowner actions are limited to resetting the boiler once or twice to see whether the code clears temporarily. Beyond that, diagnosing and replacing a temperature sensor involves accessing internal components and electrical testing that should only be carried out by a Gas Safe registered engineer. Attempting internal repairs yourself could void your warranty and create safety risks.
How much does it cost to fix fault code 58 on a Viessmann boiler?
In most cases the repair involves replacing the DHW temperature sensor or repairing the wiring, and the total cost including call-out, labour, and parts is typically in the region of £100 to £200. If the fault turns out to be a loose or corroded connector, the cost may be towards the lower end as little or no parts are needed. In the less common situation where the PCB is at fault, costs can rise significantly — typically £350 to £600 or more for a PCB replacement. If your boiler is still under warranty, a PCB fault may be covered by Viessmann at no charge, so it is worth contacting them on 01952 675000 before committing to out-of-warranty PCB work.