Error E50

Safety precautions:

1) Never work on gas or combustion parts unless you are Gas-Safe registered. If you are not qualified, limit yourself to visual checks, resets and non-invasive tasks and call an engineer for internal work. 2) Before any inspection, switch off the boiler at the electrical isolator and allow it to cool. 3) Do not attempt to alter gas connections or internal sealed components. 4) If you must access internal wiring and you are competent, isolate the mains electrical supply first; if you are unsure, stop and call a professional.

Initial checks a homeowner can do:

1) Note the exact model and serial number and take a clear photo of the fault code display. 2) Try a reset: use the boiler reset knob or button (hold for 3–5 seconds) or switch the boiler off for 30 seconds at the isolator, then restart. See if E50 clears and whether hot water is restored. 3) Run a hot tap and observe behaviour: no heat, slow heating, or fluctuating temperature. 4) Check system pressure on the gauge — if pressure is very low (<1.0 bar) some boilers will behave oddly; repressurise to the recommended pressure (around 1.2–1.5 bar) if you know how and if the boiler manual permits it. 5) Visually inspect for obvious water leaks, damaged cables or signs of corrosion around the boiler casing and nearby pipework.

Simple diagnostic checks (non-invasive):

1) If comfortable, remove the outer case only after isolating mains electricity and following the boiler manual instructions for access. Do not touch gas or combustion components. 2) Locate the DHW sensor connector/wiring harness (refer to the manual or diagram). Check the connector is fully seated and not corroded; a loose connector can cause E50. Re-seat the connector and restart the boiler to test. 3) If you have a basic multimeter and know how to use it safely, you can measure continuity of the sensor wiring to check for open circuits between the connector and the PCB. Do not attempt resistance checks across the PCB if unsure; consult the service manual for expected NTC values if you plan to measure the sensor itself.

When the fault persists or for repairs that require opening the hydraulic side:

1) If the E50 code returns after reset and basic checks, or if you find damaged wiring, corrosion, or an obviously faulty sensor, contact a qualified Gas-Safe heating engineer. 2) Replacing the DHW sensor typically requires isolating the boiler, draining the relevant part of the system, removing the cover and accessing the sensor on the heat exchanger or cylinder. Although the part is often inexpensive, the replacement involves plumbing and boiler isolation steps that should be done by a professional. 3) The engineer will verify sensor values with a multimeter, replace the sensor if required, check wiring and the PCB connections, refill and repressurise the system, and run functional tests for DHW and CH operation.

Additional practical advice:

1) Keep a record of fault occurrences, resets tried and any observations (e.g., whether CH still works). 2) Take photos of connectors and the error display to send to the engineer — this speeds diagnosis. 3) If you suspect any electrical supply issues (low voltage) or repeated unrelated fault codes, mention these to the engineer as they may indicate a PCB or wider electrical problem.

When to call a professional:

1) Call a Gas-Safe registered heating engineer if the code persists after a reset and visual checks, if you find damaged wiring, if you need the sensor replaced, or anytime work would involve gas, internal components, draining the system, or re-commissioning the boiler. 2) For safety, warranty and correct diagnosis of any possible PCB or flow-related issues behind an E50, a professional visit is advised.