How to check your boiler pressure is one of the most useful ten-minute skills a homeowner or landlord can have. A combi or system boiler that has lost pressure will stop heating, throw up a fault code and generate a call-out that, nine times out of ten, a tenant or owner could have resolved with a filling loop and a little confidence. This guide, first published in December 2023 and refreshed for 2026, explains what the gauge should read, how to top it up safely, when the problem is not the pressure at all, and what the rules in Scotland expect of a landlord when the heating fails.

How do you check your boiler pressure?

Boiler pressure is simply the pressure of the water inside a sealed central heating system, measured in bar. Too little and the pump cannot push water round the radiators, so the boiler locks out; too much and the pressure relief valve opens and dumps water outside, usually from a small copper pipe near the flue. Worcester Bosch’s guidance is that a cold system should read between 1 and 1.5 bar and will usually need topping up only once or twice a year; needing to do it more often than that is a sign of a leak or a fault that an installer should look at.

Step by step: reading and topping up the pressure

1. Find the gauge. On most modern boilers it is a small round dial, or a digital reading, on the front panel or tucked underneath. The safe zone is usually marked in green; red at the top end means over-pressure.
2. Read it cold. Switch the heating off and let the system cool for an hour or so. Pressure rises as the water heats, so a reading taken mid-cycle will be higher than the true resting figure. Cold, you want 1 to 1.5 bar.
3. Find the filling loop. This is the link between the mains cold water and the heating circuit. It is either a short braided silver hose with a valve at each end underneath the boiler, or a built-in key or lever on newer models. Your boiler’s manual, or the manufacturer’s website, shows exactly where it is and how it works for your model.
4. Top up slowly. With the boiler off, open the filling loop valves a little and watch the gauge climb. Close them when it reaches about 1.2 bar; do not chase 1.5, because the pressure will rise once the heating comes back on. If the loop is a detachable hose, close both valves firmly and remove it afterwards, as some manufacturers require.
5. Restart and reset. Turn the boiler back on and clear any low-pressure fault code if it does not clear itself. Check the gauge again after an hour of running; it should settle somewhere between 1 and 2 bar when hot.
6. If the pressure is too high. Over 2.5 bar cold, bleed one or two radiators with a radiator key until the gauge drops into the green, catching the water in a cloth. If it climbs back up on its own, or the pressure relief pipe outside is dripping, the expansion vessel or filling loop valve is probably at fault and needs an engineer.
7. Keep a note. Write the date and reading on a sticker inside the boiler cupboard. For landlords, a line in the property file is evidence of responsible management if a tenant later reports a problem.

When the pressure is not the real problem

A system that needs topping up every week has a leak, even if you cannot see one. Common culprits are a weeping radiator valve, a pinhole in a pipe under a floor, a failed expansion vessel, or a leaking heat exchanger inside the boiler. Pressure that drops only when the hot water runs usually points to a fault inside a combi boiler rather than the heating circuit. In either case, keep topping up to stay warm but book a Gas Safe registered engineer; repeated filling adds fresh, oxygenated water to the system and speeds up corrosion. Our guide to getting your home ready for a Scottish winter covers the other checks worth doing before the cold weather.

What landlords in Scotland need to know

Heating and hot water are part of the Repairing Standard, which applies to every private tenancy in Scotland. The landlord must keep the installations for heating and hot water in a reasonable state of repair and proper working order, have gas appliances checked every year by a Gas Safe registered engineer, and carry out repairs within a reasonable time once a problem is reported; a tenant who is left without heating can apply to the First-tier Tribunal’s Housing and Property Chamber. Since 6 October 2026, reported damp or mould must also be investigated within 10 working days under Scotland’s version of Awaab’s Law, and a cold, under-heated home is where condensation starts.

In practice that means three things. Show every new tenant where the gauge and filling loop are at check-in, and put a one-page note in the welcome pack, because a lock-out on a Friday night is far cheaper when the tenant can reset it. Service the boiler annually at the same visit as the gas safety check. And treat a tenant’s report of repeated pressure loss as a repair request, not a nuisance: log it, book the engineer, and keep the paperwork. Our landlord compliance checklist lists the other annual duties, and our guide to landlord registration in Scotland covers the register itself.

Honest objection: “Surely topping up the pressure is the tenant’s job”

Partly. Re-pressurising a boiler is routine user maintenance, like changing a light bulb, and a tenant who has been shown how can reasonably be expected to do it. But the landlord still owns the problem if the pressure keeps dropping, because that is a repair, and a tenancy agreement cannot contract out of the Repairing Standard. The sensible position is to make it easy for the tenant to do the simple fix, and quick for them to report anything beyond it. Landlords who manage with us get the engineer booked through our Prestwick lettings team without needing to chase.

Frequently asked questions

What should my boiler pressure be?

Between 1 and 1.5 bar when the system is cold and the heating is off, according to manufacturers such as Worcester Bosch. It will rise a little when the heating is running, typically to somewhere under 2 bar. Below about 0.5 bar most boilers will lock out and show a low-pressure fault code; above 2.5 to 3 bar the pressure relief valve will open. Check your own manual, because the exact figures vary by model.

Why does my boiler keep losing pressure?

Because water is leaving the system somewhere. The usual causes are a small leak at a radiator valve or pipe joint, a pressure relief valve that is passing water to the outside pipe, a failed expansion vessel, or a leak inside the boiler. Topping up once or twice a year is normal; weekly or monthly is not, and it should be investigated by a Gas Safe registered engineer before the corrosion from repeated fresh water damages the boiler.

Is it safe to repressurise a boiler myself?

Yes, for the filling loop on a sealed system; it is designed to be used by the householder and involves no gas work. Keep the boiler off while you do it, open the valves slowly, stop at about 1.2 bar, and close the valves fully afterwards. Anything that involves opening the boiler casing, the gas supply or the flue is work for a Gas Safe registered engineer only, and in a rented home the landlord should arrange it.

Who is responsible for the boiler in a rented property in Scotland?

The landlord. Under the Repairing Standard the heating and hot water installations must be kept in proper working order, gas appliances must have an annual safety check by a Gas Safe registered engineer, and repairs must be done within a reasonable time of being reported. The tenant’s part is to use the system sensibly, report problems promptly and, if shown how, reset a low-pressure lock-out. Our guide to letting agent fees in Scotland explains what a managed service covers when something does go wrong.

How often should a boiler be serviced?

Once a year. For a landlord in Scotland the annual gas safety check is a legal requirement and the service is usually done at the same visit; for an owner-occupier it is the condition of most manufacturers’ warranties and the best way to catch a slow leak or a tired expansion vessel before winter. Book it for late summer or early autumn, when engineers are less stretched than in the first cold snap.

Need a hand with a rented property?

Lomond’s lettings team manages homes across Ayrshire and Glasgow, with gas safety checks, servicing and repairs handled through vetted local engineers. Find out what full management includes on our let your property page, read our landlord information, or browse more landlord and lettings guides.

This article is general information, not legal or financial advice. Property rules differ across Scotland and the rest of the UK and change over time; check the current position with a solicitor or the relevant council before acting. Last verified: 26 October 2026 against mygov.scot (repair standards for private tenants) and Worcester Bosch’s heating system pressure guidance.

Blocked sinks and drains are the other winter call every landlord gets; our guide to how to unclog a drain covers the safe fixes and who is responsible for the repair in Scotland.