58 Error on Viessmann Boiler? Comprehensive Fix Guide

How to Fix Viessmann Error 58 (Step-by-Step)

Step 1: Safety First & Power Down
Before you even touch a screwdriver, you must ensure the unit is safe. Locate the power switch (usually a fused spur near the boiler) and turn it off. For extra safety, flip the circuit breaker in your main panel. Never work on a live boiler. Wait about 10 minutes for the internal components to cool down so you don’t burn your hands on the internal pipework.

Step 2: Open the Front Casing
Most Viessmann Vitodens models have two screws at the bottom of the front panel. Using your Phillips head screwdriver, loosen these (they often stay attached to the panel so you don’t lose them). Once loosened, gently pull the bottom of the panel toward you and lift it up off the top hooks. Set the panel aside in a safe place where it won’t get scratched.

Step 3: Locate the DHW Sensor
Look for the Domestic Hot Water pipe (usually one of the copper pipes leading to your hot water tank or the plate heat exchanger). You are looking for a small sensor clipped onto the pipe or screwed into a pocket. It will have two thin wires (often blue, grey, or black) leading back to the main control box. This is your target.

Step 4: Inspect the Wiring Harness
Trace the wires from the sensor all the way back to the control board. Look for any obvious signs of fraying, kinks, or those pesky rodent chew marks. If the wire looks damaged, you may be able to strip the ends and use a crimp connector to bridge the gap, but replacing the entire sensor lead is always the more reliable “pro” move.

Step 5: The Multimeter Test (The “Smoking Gun”)
Unplug the sensor from the wiring harness. Set your multimeter to the Ohms (Ω) setting. Place your probes on the two pins of the sensor.

• If the multimeter reads “OL” (Open Loop) or “1”, the sensor is dead—the internal lead is broken.
• If it gives you a reading (usually between 5k and 20k ohms depending on temperature), the sensor might be okay, and the fault lies in the wiring or the control board.

Safety Warning: Do not touch any of the gas valves or gas-carrying components while performing this test.

Step 6: Replacing the Sensor
If the test confirmed a break, use your needle-nose pliers to gently unclip the old sensor. If it’s a “wet” sensor (screwed into the water), you will need to drain that section of the system first—but most modern Viessmanns use “clip-on” sensors. Clip the new sensor onto the pipe in the exact same spot, ensuring it has a tight, flush fit against the metal. Plug the electrical connector back in until you hear a satisfying “click.”

Step 7: Reassemble and Reset
Put the front cover back on and tighten those bottom screws. Restore power to the boiler. You may need to press the “Reset” button on the control panel. If the repair was successful, Error 58 will vanish, and you’ll hear the boiler begin its ignition sequence. Congratulations, you’ve brought the heat back!

Detailed Diagnosis: Root Causes

Why did this happen? It’s rarely “bad luck” and usually down to the physics of your heating system. Here are the three most likely reasons your lead has “broken”:

1. Thermal Fatigue of the NTC Thermistor: The DHW sensor is an NTC (Negative Temperature Coefficient) thermistor. It lives in a world of constant temperature swings—from freezing cold to 140°F (60°C) dozens of times a day. Over several years, these temperature fluctuations cause the internal components of the sensor to expand and contract until the delicate internal connection literally snaps. This creates the “lead break” the error describes.

2. Corrosion at the Connection Points: Boilers are high-moisture environments. If there has been even a tiny bit of weeping from a pipe or condensation buildup, moisture can find its way into the electrical plug that connects the sensor to the wiring harness. This leads to oxidation (green or white crusty buildup), which increases electrical resistance until the control board thinks the wire has been cut entirely.

3. External Wire Damage (The “Rodent Factor”): If your boiler is located in a garage, attic, or basement, it’s not uncommon for small rodents to find the warmth of the boiler casing inviting. Unfortunately, they also find the soy-based insulation on modern wires quite tasty. A single tiny chew mark can sever the signal wire, triggering Error 58 instantly.

Symptoms of Viessmann Error 58

Before we dive into the guts of the machine, let’s confirm what you’re seeing. This error doesn’t always behave the same way for everyone, but here are the classic signs that your DHW sensor is the culprit:

• The Digital “Red Flag”: Your boiler’s control panel is flashing the code “58” or “Fault 58,” often accompanied by a red warning light.
• The Lukewarm Surprise: You might have had hot water for a minute, but it quickly turned cold. This happens because the boiler tried to fire up, realized it couldn’t monitor the temperature safely, and cut the burner.
• Pump Activity but No Flame: You might hear the internal pump whirring or the fan spinning, but you never hear the “whoosh” of the gas igniting.
• Short Cycling: The boiler turns on for 5-10 seconds and then shuts down immediately, repeating this cycle endlessly as it struggles to find a signal from the sensor.

How to Prevent Error 58

Once you’ve fixed the issue, you definitely don’t want to see that “58” staring at you again next winter. Here is how to keep your boiler’s sensors in tip-top shape:

• Annual Professional Service: A Gas Safe engineer doesn’t just check for leaks; they also clean the internal dust and check for signs of moisture buildup that leads to sensor corrosion. This is the single best way to catch a failing sensor before it leaves you with a cold shower.
• Use Dielectric Grease: When installing a new sensor, a tiny dab of dielectric grease on the electrical terminals can prevent moisture from reaching the metal. This acts as a shield against oxidation and ensures a solid connection for years to come.
• Vibration Dampening: Ensure the wiring harness is secured with cable ties and isn’t resting against a vibrating pump or a hot pipe. Constant vibration can rub the insulation thin over time, leading to a short or a break.

Frequently Asked Questions

Q: Can I run my boiler while Error 58 is active?
A: Technically, your central heating (radiators) might still work on some Viessmann models even if the DHW sensor fails, but most modern units will lock out entirely as a safety precaution. It is not recommended to “force” the boiler to run; it’s best to fix the sensor first to avoid overheating the domestic water circuit.

Q: Is Error 58 the same as Error 51?
A: Not quite! While both relate to the DHW sensor, Error 58 specifically means a “break” or open circuit (no signal). Error 51 usually refers to a “short circuit” (signal is too high). Both usually require a sensor replacement, but they indicate different types of electrical failure.

Q: How do I know which sensor to buy?
A: You’ll need your boiler’s serial number (usually found on top of the casing or behind the drop-down flap). Viessmann uses specific NTC sensors for different models. Search for “Viessmann NTC Sensor” followed by your model name (e.g., Vitodens 100-W) to ensure the resistance curve matches what your control board expects.