Common problems guide

The most common Alpha Pro Tec 24 problems

The faults most likely to send a Alpha Pro Tec 24 into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.
53 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
E04 High DIY-safe

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

What to try first

Locate the filling loop (a silver flexi-hose) beneath the boiler.Open the valves on the filling loop to allow cold mains water to enter the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone, ideally 1.5 bar.Close both valves tightly and remove the filling loop if required.

Est. cost
£80-120
Parts
Water pressure switch, Pressure relief valve, Expansion vessel
Full guide for E04
02
E10 High DIY-safe

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

What to try first

Locate the external filling loop, which is usually a flexible silver braided hose with one or two valves located underneath the boiler.Open the valves slowly to allow mains water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close both valves tightly immediately once the correct pressure is reached to prevent over-pressurisation.

Est. cost
£80-150
Parts
Pressure relief valve, Pressure sensor, Expansion vessel
Full guide for E10
03
0E37 High DIY-safe

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

What to try first

Locate the internal filling loop, which is usually a small silver braided hose or a plastic key located underneath the boiler.Open the filling valve slowly to let water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close the valve tightly to stop the flow of water and ensure the boiler resets itself automatically.

Est. cost
£0-£100
Parts
Pressure relief valve, Expansion vessel, Filling loop
Full guide for 0E37
04
E01 High Engineer

Your boiler has failed to light the flame needed to heat your water and home, so it has automatically shut down for safety.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for E01
05
E02 High Engineer

Your boiler has detected that it is running too hot and has automatically turned itself off to prevent any damage or danger.

Est. cost
£120-250
Parts
Overheat thermostat, Central heating pump, Diverter valve
Full guide for E02
06
E05 High Engineer

Your boiler's temperature sensor is providing incorrect readings, which prevents the unit from heating your water or home safely.

Est. cost
£120-220
Parts
Flow NTC sensor, Wiring harness
Full guide for E05
Parts most often replaced

on the Alpha Pro Tec 24

Water pressure switchPressure relief valveExpansion vesselPressure sensorFilling loopIgnition electrode

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Alpha shows an Emergency or High severity code
  • The boiler keeps locking out after repeated resets
  • You've tried the DIY checks and the fault hasn't cleared
  • There's visible water leaking from the boiler
  • The flame is yellow or orange instead of blue
See the full 53-code list for the Alpha Pro Tec 24

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →