BoilerFaultCodesYour boiler has detected low water pressure in the system, which means it cannot circulate enough water to heat your home or provide hot water safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: ALTERNATING 'H' '4' GO TO FRAME 93
What causes this fault?
This fault occurs when the water pressure inside your heating system drops below a safe operating level, usually because water has escaped through a small leak or air was bled from the radiators. Without enough pressure, the boiler cannot move water around your pipes to heat your home, so it shuts down to prevent internal damage. The most common reasons are a leaking radiator valve, a failing expansion vessel, or a dripping pressure relief valve.
This issue is more common in autumn when homeowners turn their heating back on for the first time, as the system settles and reveals any pressure lost during the summer months.
DIY fix possible
Locate the filling loop (usually a silver braided hose with small black valves underneath or near the boiler).Slowly open the valve(s) until you hear water flowing and the pressure gauge rises to 1.5 bar (the green section).Close the valves tightly and press the 'Restart' or 'Reset' button on the control panel.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like H4 — no call-out fees, no surprises.
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Ideal Esprit HE is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
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