Baxi Boiler E50 Error Code: Causes & Fixes

If you have woken up to cold showers and a flashing control panel, you are likely dealing with the Baxi boiler E50 error code. This specific fault is a common occurrence across the Baxi range, including the popular Platinum, Duo-tec, and 600 Combi models. 

In the world of home heating, this code is the system’s way of telling you that there is a breakdown in communication regarding your hot water temperature.

The baxi boiler E50 error code specifically points to a “Domestic Hot Water (DHW) NTC Thermistor” fault. Essentially, the sensor responsible for monitoring the temperature of the water heading to your taps is either sending incorrect data or no data at all to the Printed Circuit Board (PCB). 

While this might sound technical, understanding the root causes can help you decide whether you can resolve it with a simple reset or if you need to call in a Gas Safe registered engineer.

What does the Baxi boiler E50 error code mean?

The Baxi boiler E50 error code means that your boiler has detected a fault with the Domestic Hot Water (DHW) NTC thermistor, which is a sensor that measures temperature changes. When this “Negative Temperature Coefficient” (NTC) sensor fails, the boiler cannot safely determine how hot the water is, leading to a lockout for safety reasons.

In most instances, the baxi boiler E50 error code results in the boiler refusing to provide hot water, though your central heating might still function in some scenarios. 

The resistance in an NTC thermistor decreases as the temperature rises; if the PCB detects a resistance level that is “out of range” (either a short circuit or an open circuit), it triggers the E50 lockout to prevent scalding or internal component damage.

What are the main causes of the E50 fault?

The Baxi boiler E50 error code is primarily caused by a defective DHW thermistor, damaged wiring, or, in more complex cases, a malfunctioning main circuit board. Because the sensor is constantly exposed to temperature fluctuations and moisture, it is a high-wear component that can degrade over time.

1. Defective DHW NTC Thermistor

The most frequent culprit behind the baxi boiler E50 error code is a sensor that has simply reached the end of its lifespan. Over several years, the internal components of the thermistor can fail, or limescale buildup on the sensor pocket can insulate it, leading to inaccurate readings.

How to fix a defective sensor:

1. Perform a Reset: Before replacing parts, press and hold the ‘R’ or reset button for five seconds. Sometimes a temporary glitch triggers the code.
2. Isolate the Power: If the code returns, a professional must turn off the electrical supply to the boiler.
3. Test Resistance: An engineer will use a multimeter to check the ohms (resistance) of the sensor against the manufacturer’s data chart.
4. Drain the Secondary Circuit: If the sensor is a “wet” type, the hot water circuit must be drained.
5. Replace the Part: Unscrew the old thermistor and install a genuine Baxi replacement part.
6. Refill and Test: The system is repressed, and the boiler is fired up to ensure hot water returns.

2. Damaged or Corroded Wiring

If the sensor itself is healthy, the baxi boiler E50 error code may be triggered by the “loom” or wiring connecting the sensor to the PCB. Vibration from the pump or moisture from a small internal leak can cause wires to fray or connections to corrode.

How to fix wiring issues:

1. Visual Inspection: A technician will inspect the cables leading from the DHW sensor for signs of burning, fraying, or green copper corrosion.
2. Check Connections: Ensure the multi-plug connectors are firmly seated on both the sensor and the PCB terminals.
3. Continuity Testing: Using a multimeter, the engineer will check for a continuous electrical path.
4. Clean Terminals: If corrosion is present, cleaning the contact points with electrical contact cleaner may resolve the issue.
5. Replace Wiring Loom: If the wires are snapped or badly damaged, a new wiring harness section must be installed.

3. Faulty Printed Circuit Board (PCB)

In rarer circumstances, the baxi boiler E50 error code appears because the “brain” of the boiler (the PCB) can no longer interpret the signal from the sensor. This is usually the last resort diagnosis if the sensor and wiring both test perfectly.

How to fix a PCB fault:

1. Confirm External Components: The engineer will verify that the NTC sensor and wiring are 100% functional first.
2. Voltage Check: Check the voltage output from the PCB to the sensor circuit.
3. Software Check: On modern Baxi 600 or 800 models, ensure the parameters haven’t been corrupted.
4. Replace the PCB: If the board is confirmed dead, a new PCB must be fitted and programmed with the specific boiler’s “firmware” or parameter settings.

Can I fix the E50 error code myself?

No, you should not attempt to fix the Baxi boiler E50 error code yourself beyond a simple reset, as it involves accessing the internal electrical components of a gas appliance. Under UK law, any repair that requires removing the boiler casing must be performed by a Gas Safe registered engineer to ensure the unit remains room-sealed and safe.

While a DIY enthusiast might feel confident replacing a clip-on sensor, the risks of incorrect installation or disturbing gas-carrying components are significant. Always check your engineer’s ID card to ensure they are qualified for “Boilers” and “Water Heaters.”

Is it time to replace your old Baxi boiler?

If you are frequently seeing the Baxi boiler E50 error code alongside other faults like E119 (low pressure) or E133 (ignition failure), your appliance may be reaching the end of its reliable service life. 

Repairing an older boiler can often become a “false economy” where the cost of parts and labour quickly approaches the price of a modern, energy-efficient replacement.

Investing in a new A-rated boiler can save you up to £540 a year on your energy bills while providing the peace of mind that comes with a long manufacturer warranty. If your Baxi is over 10–12 years old and keeps breaking down, it is worth exploring your options.

Would you like to get a fixed-price, no-obligation quote for a brand-new, high-efficiency boiler? Request a new boiler quote from Boilers 2 Go today and enjoy reliable heating for years to come.

FAQs

How much does it cost to fix an E50 fault in the UK?

The cost generally ranges between £80 and £150. This usually covers the Call-out fee plus the cost of a new NTC thermistor, which is a relatively inexpensive part (typically £15–£30). If the PCB needs replacing, the cost can jump to over £300.

Will my home insurance cover the E50 repair?

Most standard home insurance policies do not cover boiler repairs unless you have specific Emergency Home Cover or a dedicated boiler maintenance plan. Check your policy schedule for “Gas Supply and Boiler” sections.

Can a frozen pipe cause the E50 code?

Usually, no. Frozen condensate pipes typically trigger an E28 or E133 code. The E50 is strictly related to the hot water temperature sensor circuit, though extreme cold can sometimes affect older external wiring.

How long does a Baxi NTC sensor usually last?

On average, an NTC thermistor lasts between 6 and 10 years. Their lifespan is often shortened in “hard water” areas (like the South East of England) where limescale buildup can cause the sensor to overheat and fail prematurely.

Does an E50 error mean my boiler is leaking?

Not necessarily, but the two can be linked. If an internal leak from the heat exchanger or a seal drips onto the DHW sensor wiring, it can cause a short circuit that triggers the E50 code. An engineer will check for moisture during the repair.