Error code
Ideal Boiler Fault Code D4
System water pressure is too low The most likely cause is pressure dropped below the normal operating range. Check first: if the boiler allows user repressurising, follow only the official filling loop method.
Quick answer
D4: what does it mean and how to fix
What does it mean?
System water pressure is too low
How to fix first
Check the pressure gauge against the manufacturer guidance in the manual.
Why is this happening?
Pressure dropped below the normal operating range
When should I call an engineer?
If pressure repeatedly drops or you notice leaks, arrange a qualified heating engineer.
What does this error code mean?
Ideal boiler fault code D4 usually means the boiler has detected low system pressure and locked out to protect the heating circuit.
In practice, D4 is commonly linked to Pressure dropped below the normal operating range, Recent radiator bleeding or maintenance, or Ongoing water loss from a leak.
Start with this safe check: Check the pressure gauge against the manufacturer guidance in the manual. If the code returns, the fault worsens, or the appliance does not behave normally, if pressure repeatedly drops or you notice leaks, arrange a qualified heating engineer.
Why is this happening?
- Pressure dropped below the normal operating range
- Recent radiator bleeding or maintenance
- Ongoing water loss from a leak
How to fix this safely
- 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.
Reset steps
- 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 low-pressure fault codes
Relevant guide
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.