Over Pressurization in Boilers – An Overview

For a boiler to work efficiently, the pressure inside it must be maintained typically between 1 and 1.3 bar. If the boiler reaches extremely high pressure, a relief valve is triggered that helps prevent over pressurization. However, if the relief valve is faulty or jammed, the boiler does not work effectively and leads to damage. You might want to call a boiler repairman, click here for one.

Pressure Gauge

A pressure gauge is installed on top of a boiler. It may be either analog or digital.

An analog gauge is equipped with needles like a clock or speedometer. It has a range of pressure values around the edge while the ideal range of pressure is highlighted. The needle points to the current state of pressure.

A digital gauge is equipped with an LCD, LED, or screen for display. It may also be used to display other information such as timers, temperatures, or whether the boiler is working for central heating or hot water.


In case of a faulty pressure gauge, leakage may occur from the central heating. The leakage starts usually at the joints. Therefore, if there is any suspicion about leakage, pressure gauge must be evaluated.

How to reduce boiler pressure?

Once high pressure in a boiler is diagnosed, steps must be taken to reduce it. Some of the techniques to resolve over pressurization in boilers are listed below:

1. Filter valve

Filter valves are placed between the last radiator and the boiler. Water passes through these valves for filtration. In addition, it serves as a drainage valve to relieve pressure in the boiler. The valve can be opened to release pressure but make sure to put a bucket underneath for draining liquid.

2. Drain valve

Some of the boilers are equipped with drain-off valves instead of a filter valve. They are typically Y-shaped or T-shaped components placed near the pipework. Draining the valve also releases pressure inside the boiler

3. Radiator Drainage

Draining the radiator may also help release pressure inside the boiler. In addition to air pressure, it also helps lower the water pressure.

4. Undo a radiator nut

Although this is a specialist task, it is also one of the effective ways of releasing pressure inside the boiler. Using a spanner, the nut must be gently twisted. Water may spill out so it is important to have preparations to counter it.

Preventing high pressure from coming back

After the release of pressure using the above-mentioned procedures, it must be investigated why the pressure was increased in the first place.


The filling loop exists where water enters the system and comprises two valves. The pressure increases, when both valves are open. Therefore, it must be checked if these valves are left open by accident.

Sometimes the two valves are connected by a hose. There is a possibility of the hose not connected properly which may also affect the pressure inside the boiler.

Overfilling of water in the filling loop may also lead to increased pressure.

Additionally, a faulty expansion vessel may also be the reason behind high pressure. Although the expansion valve helps in maintaining the pressure a fault in the valve or damage can lead to raised pressure inside a boiler.

Salman Zafar

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