How to repressurise a boiler safely using the filling loop

Detail that affects your quote for repressurising a boiler

• Always repressurise with the boiler off and the system cold
• Target the figure on the boiler's data plate, usually 1 to 1.5 bar
• Close both filling loop valves fully once you reach that figure
• A loop left slightly open causes pressure to creep up overnight
• Pressure that will not hold points to a leak, not a filling technique

How we read repressurising a boiler on site

With the boiler off and the system cold, open both filling loop valves slowly and watch the gauge climb, aiming for the figure printed on the boiler's data plate, typically between 1 and 1.5 bar for most domestic systems. Close both valves the moment you reach that figure, since leaving either one even slightly open lets pressure creep upward over the following hours as the loop weeps. If the needle will not move, or it climbs and then falls straight back down again, stop and treat that as a sign of a leak or a stuck valve rather than repeating the process.

Where we deal with this

• Heytesbury (BA12) · 15 mi
• Lansdown (BA1) · 9 mi
• Bathampton (BA2) · 9 mi
• Freshford (BA2) · 7 mi

Questions we get asked

What if I do not have a filling loop?

Some boilers use an internal or keyed filling device instead. Do not force an unfamiliar valve; ask us to show you the correct method on a visit.

How often is it normal to need to do this?

Once or twice a year is unremarkable. More frequent top-ups mean water is leaving the system and the cause needs finding.

Can I overfill the system?

Yes, and doing so can trigger the pressure relief valve to discharge outside. If the gauge overshoots, bleed a radiator slightly to bring it back down rather than leaving it high.