Error F.73

Safety first:

1) If you are not a qualified Gas Safe or qualified appliance technician do not open the boiler case or attempt electrical or gas repairs. Working inside a boiler can be dangerous and illegal for unqualified persons. 2) If you smell gas, leave the property immediately and contact your gas emergency number. 3) Isolate power to the boiler before opening the casing (but only do this if you are qualified and confident; homeowners should not open the casing).

Initial basic checks a homeowner can safely do:

1) Check the front display and take note of the exact fault code F.73 and any other codes or messages. 2) Check the system pressure gauge on the boiler. Normal cold system pressure is typically around 1.0–1.5 bar for most domestic combi systems. If pressure is below about 0.8–1.0 bar, topping up is appropriate. 3) Top up the system using the filling loop or the two small valves/handles under the boiler if you know how: open the valve(s) slowly, watch the pressure gauge and stop at around 1.0–1.5 bar, then close the valve(s). Only use the filling loop supplied with your system and follow your boiler’s user guide. 4) After topping up, try a normal boiler reset (use the reset button or the procedure in your manual) and see if the F.73 clears. If the boiler remains locked with F.73, do not repeatedly attempt resets.

Visual inspection homeowners can perform (no internal opening):

1) Look for visible signs of leakage or water corrosion beneath the boiler or around pipe connections. A slow leak around the pressure sensor area often causes corrosion on the electrical connector. 2) Check for water on or around the wiring visible outside the casing and any obvious disconnected plug (do not unplug or replug internal connectors unless you are qualified). 3) Photograph any wet areas, corroded connectors or loose pipes—these images will help the engineer diagnose the fault quickly.

Basic diagnostic steps that may be performed by a qualified engineer (do not attempt unless competent):

1) The engineer will isolate power and open the casing to inspect the pressure sensor, its electrical connector and the wiring harness for corrosion, water ingress or damage. 2) They will test the sensor electrical signal at the connector (voltage or mV/resistance depending on sensor type) and check continuity back to the PCB. A 0V or short to ground indicates wiring/connector or sensor fault; an open or erratic value suggests a failed sensor. 3) If the sensor port is clogged with magnetite/debris the sensor may misread; the engineer may clean or reposition the sensor or remove magnetite buildup and fit a screen or move the sensor to the improved position used on later models. 4) If wiring is corroded, they may repair or replace the connector or wiring harness. 5) If the PCB input stage is damaged, further PCB diagnostics or replacement may be needed.

Practical fixes and what to expect from the engineer:

1) If the system was simply low on water pressure, topping up and resetting will usually clear the fault and no further work is needed, but the cause of pressure loss (leak, radiator bleed, expansion vessel issue) should be checked. 2) If the pressure sensor has failed or its connector is corroded, the typical repair is sensor replacement and/or wiring connector repair or harness replacement. 3) If water has corroded the connector, cleaning may temporarily restore communication, but replacement of corroded parts is the safer long-term fix. 4) In a minority of cases a PCB fault may be present and the engineer will advise on PCB repair or replacement.

When to call a professional and urgency:

1) If topping up and a single reset do not clear F.73, call a Gas Safe registered heating engineer promptly. 2) If you see signs of water leak or corroded electrical connectors, arrange a visit sooner rather than later—continued water ingress can cause wider electrical damage. 3) Do not try to replace the sensor, wiring or PCB yourself unless you are a qualified engineer; incorrect repairs risk appliance damage, gas safety issues and may invalidate warranty or insurance.

What to tell the engineer when booking:

1) Report the exact fault code (F.73) and any other codes, what the pressure gauge reads, whether topping up was attempted and whether the boiler reset. 2) Mention any visible leaks, corrosion, or if the fault is intermittent. 3) Provide the boiler model (EcoTEC Pro or EcoTEC Plus), serial number if available, and recent service history.

Summary recommendation: Perform the simple safe checks described above (check pressure, top up correctly, attempt one reset). If F.73 persists or you find leakage/corrosion, stop and call a Gas Safe registered engineer to diagnose and repair the pressure sensor, wiring/corroded connector, or PCB as required.