Error code
Ideal Boiler Fault Code D4
Quick answer
D4
System water pressure is too low
First safe action
Check the pressure gauge against the manufacturer guidance in the manual.
Meaning
Ideal boiler fault code D4 usually means the boiler has detected low system pressure and locked out to protect the heating circuit.
Likely causes
- Pressure dropped below the normal operating range
- Recent radiator bleeding or maintenance
- Ongoing water loss from a leak
Safe first checks
- Check the pressure gauge against the manufacturer guidance in the manual.
- If the boiler allows user repressurising, follow only the official filling loop method.
- Stop if pressure drops again quickly after topping up.
How to reset
- Reset the boiler only after the pressure has been restored to the correct range.
- Do not keep resetting if the pressure immediately falls again.
When to call an engineer
If pressure repeatedly drops or you notice leaks, arrange a qualified heating engineer.
Safety warning
Do not remove the boiler casing or attempt internal repairs. Use only the manufacturer-approved repressurising method, and book a qualified heating engineer if pressure keeps falling.
Useful hub links
Related fault codes
C5 for Ideal Boiler
Fan, flue, or air pressure sensing problem
C6 for Ideal Boiler
Fan, flue, or air pressure sensing problem
C7 for Ideal Boiler
Control board or internal communication fault
F1 for Ideal Boiler
System water pressure is too low
F2 for Ideal Boiler
Flame detection has been lost during operation
F3 for Ideal Boiler
Fan, flue, or air pressure sensing problem
Relevant guides
Frequently asked questions
Can I keep resetting a Ideal boiler with D4?+
No. If D4 returns after one standard user reset, stop there and arrange a qualified engineer if the manual gives no safe next step.
Is D4 something I can repair myself?+
Boiler faults should be treated cautiously. Stay within the user checks in the manual, and leave gas, combustion, and internal boiler repairs to a qualified professional.