BoilerFaultCodesSime P 04 Fault Code
Also written as P04 — same fault.
The Sime P 04 fault code means: your boiler has stopped working because the water pressure inside the heating system has dropped too low.. It appears on 1 Sime model in our database.
Technical description: Low pressure
DIY fix possible
Locate the filling loop, which is a silver braided hose with one or two valves connecting your mains water to your heating pipes.Open the valve(s) 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 the valve(s) tightly and check that the error code has cleared.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like P 04: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Sime models that show the P 04 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Sime P 04 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026