Ideal Logic Max Heat Fault codes & diagnostics

36 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Regular Natural Gas 15-30 kW 2018-present
GC Numbers 41-796-1741-796-1841-796-1941-796-2041-796-21
Download the Ideal Logic Max Heat manual The official installation & service manual (PDF) — the exact document these fault codes were verified against. PDF

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
11 High 3 Medium 1 Low 21 Unrated
Versions & GC numbers

Which version do you have?

The GC number on your boiler's data badge identifies the exact appliance and production years, as recorded in the UK Product Characteristics Database.

GC number Appliance (register name) Produced
41-796-17 LOGIC MAX HEAT H12 2018–present
41-796-18 LOGIC MAX HEAT H15 2018–present
41-796-19 LOGIC MAX HEAT H18 2018–present
41-796-20 LOGIC MAX HEAT H24 2018–present
41-796-21 LOGIC MAX HEAT H30 2018–present

Appliance names and production years are taken from the UK Product Characteristics Database (the SAP/SEDBUK register). Where a GC number is also printed in this model's own manufacturer manual, both sources were checked to agree.

Just want the most common Ideal Logic Max Heat faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 36 documented codes

Tap any card for details

4.2

Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.

High DIY-safe £100-£350

What to check first

  1. Check that all radiator valves are fully open to allow water to circulate.
  2. Ensure there is enough pressure in the system by checking the pressure gauge (aim for 1.5 bar).
  3. Press the 'Reset' button on the front of the boiler panel once the unit has cooled down.

Parts commonly replaced

  • Circulation Pump
  • Overheat Thermostat
  • Thermistor
Full explanation for 4.2
4.3

Your boiler is failing to light the gas to create heat, so the system has shut itself down for safety.

High DIY-safe £100-£350

What to check first

  1. Check if other gas appliances, like a cooker, are working to confirm gas supply.
  2. If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen.
  3. Press the 'Reset' button on the boiler control panel once.

Parts commonly replaced

  • Ignition electrode
  • Spark generator
  • Gas valve
  • Flame sensing cable

Related codes

Full explanation for 4.3
4.4

Your boiler has detected that there is not enough water pressure or water is not moving through the system properly to operate safely.

High DIY-safe £100-280

What to check first

  1. Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.
  2. If the pressure is low, use the filling loop handles underneath the boiler to top it up until the needle reaches the green zone.
  3. Ensure all radiator valves and isolation valves under the boiler are fully open.
  4. Reset the boiler by turning the control knob to 'RE' or pressing the reset button.

Parts commonly replaced

  • Circulating Pump
  • Water Pressure Sensor
  • Automatic Air Vent
Full explanation for 4.4
4.5

Your boiler is failing to keep its flame lit, which means it cannot heat your home or water.

High DIY-safe £120-300

What to check first

  1. Check if other gas appliances in your home, like a hob, are working correctly
  2. Ensure your gas meter has credit if you use a pre-payment meter
  3. Restart the boiler by pressing the 'Reset' button

Parts commonly replaced

  • Flame sensing electrode
  • Gas valve
  • Ignition lead
Full explanation for 4.5
4.6

Your boiler's fan, which safely pushes exhaust gases out of the flue, has stopped working correctly and is preventing the boiler from firing up.

High Engineer only £250-450

Parts commonly replaced

  • Fan assembly
  • Printed Circuit Board (PCB)
  • Wiring harness
Full explanation for 4.6
4.7

Your boiler detects a flame when it should be off, which is a safety error that prevents the system from starting up.

High Engineer only £180-450

Parts commonly replaced

  • Gas Valve
  • Ionisation Lead
  • Main PCB
Full explanation for 4.7
4.8

Your boiler has lost its ability to measure the temperature of the water leaving the unit, meaning it cannot safely regulate the heat.

High Engineer only £120-190

Parts commonly replaced

  • Flow Thermistor (NTC Sensor)
  • Wiring Harness
  • Main PCB
Full explanation for 4.8
4.9

Your boiler has detected an issue with a temperature sensor that monitors the water returning from your radiators, often resulting in the system shutting down for safety.

High Engineer only £100-180

Parts commonly replaced

  • Return Thermistor (NTC Sensor)
  • Wiring Harness

Related codes

Full explanation for 4.9
4.10

Your boiler has lost communication with the sensor that measures the temperature outdoors, which may cause your heating to run less efficiently.

Low Engineer only £90-180

Parts commonly replaced

  • Outside Weather Compensation Sensor
  • Sensor Wiring

Related codes

Full explanation for 4.10
4.11

Your boiler is not providing central heating even though it may still be providing hot water.

High DIY-safe £100-250

What to check first

  1. Check that your room thermostat or programmer is set higher than the current room temperature
  2. Ensure the heating mode is active on the boiler display
  3. Check that the radiator valves are open and not turned to zero

Parts commonly replaced

  • External Thermostat
  • Motorised Diverter Valve Head
  • Printed Circuit Board (PCB)
Full explanation for 4.11
Showing 11–20 of 36
4.12

Your boiler is providing central heating as normal, but it is currently unable to heat your hot water.

Medium Engineer only £140-£280

Parts commonly replaced

  • Plate Heat Exchanger
  • Diverter Valve Motor
  • DHW Temperature Sensor
  • Flow Turbine
Full explanation for 4.12
4.13

Your boiler has lost power or the screen has failed, meaning it will not operate and you cannot see any settings or status messages.

High DIY-safe £100-350

What to check first

  1. Check if other appliances in the house are working to rule out a general power cut
  2. Check your home's main fuse box (consumer unit) to see if a circuit has tripped
  3. Ensure the boiler's power switch (usually a fused spur near the unit) is turned on

Parts commonly replaced

  • Display PCB
  • Main Control PCB
  • Internal Fuse
Full explanation for 4.13
4.14

Your boiler is providing hot water to your cylinder correctly, but the central heating for your radiators is not working.

Medium DIY-safe £120-250

What to check first

  1. Check that your room thermostat or heating programmer is turned up and calling for heat
  2. Ensure any zone valves (usually found in the airing cupboard) are moving correctly
  3. Reset the boiler by turning the control knob to 'Reset' and then back to the original position

Parts commonly replaced

  • External Zone Valve
  • Room Thermostat
  • Wiring Centre

Related codes

Full explanation for 4.14
4.15

Your boiler is providing central heating for your radiators as normal, but is failing to heat your hot water tank or taps.

Medium Engineer only £180-350

Parts commonly replaced

  • Diverter Valve Actuator
  • DHW Flow Sensor
  • External Cylinder Thermostat

Related codes

Full explanation for 4.15
Showing 21–30 of 36
Fd

Your boiler has stopped working because it cannot detect water moving through the system to keep it running safely.

High DIY-safe £100-£350

What to check first

  1. Check that your external heating valves or isolation valves are fully open.
  2. Ensure your radiator valves (TRVs) are turned up and not all closed.
  3. Check the boiler pressure gauge and top it up to 1.5 bar if it is too low.
  4. Gently bleed your radiators to remove any trapped air pockets.

Parts commonly replaced

  • Circulation Pump
  • Pump Head
  • Flow Pipe Thermistor
Full explanation for Fd
Showing 31–36 of 36
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