Everything You Need To Know About Boiler Pressure

San Rafael

(415) 942-6565

Santa Rosa

(707) 452-3464

Your boiler is an integral part of your central heating system. It heats the water inside the tank that supplies either steam or hot water (most modern systems are hot water heating systems. Older homes usually have steam heating systems), which flows through the pipes and radiators.

What is Boiler Pressure?

Boiler pressure is the pressure of hot water running in your central heating system. Your boiler must be at the right pressure for your heating system to work properly. Usually, the ideal boiler pressure is between 1-1.5 bars (when your central heating is not working) and 1-2 bars (when your boiler is heating up).

Boilers have a boiler pressure gauge (usually located on the front of the boiler or behind the control panel) that displays boiler pressure. On older systems, the boiler pressure gauge is usually located underneath as part of the pipework. Boiler pressure dials indicate low and high boiler pressure with red and green color-coded markers. Safe levels of boiler pressure are marked in green.

It is normal for boiler pressure to rise when the boiler is hot and falls as it cools down (water expands when heated and contracts when cooled). However, an abnormal rise or drop in boiler pressure could indicate a problem with your boiler.

If your boiler pressure is too low, your system won’t be able to heat water properly or, worse, won’t heat your water at all. If, on the other hand, your boiler pressure is too high, your system may fail.

Low Boiler Pressure

Sometimes, a boiler gradually loses pressure over time. You know you have low boiler pressure when it drops below one bar. Two common causes of low boiler pressure are water leaks and bleeding radiators.

Water Leaks

A leak in your pipe boiler or radiators could be hard to spot. Look around for signs of leaks such as damp patches and drips of water around the base of the boiler. Damp patches along the pipework could indicate problems with your pipework. Do not try to look inside your boiler. If you are unable to diagnose the problem, reach out to an expert for help.

Bleeding Radiators

If you just bled your radiators, you may notice a drop in your boiler pressure. Bleeding the radiators will remove air in your boiler, causing your boiler pressure to drop.

How to Increase Boiler Pressure?

Follow these steps to increase your boiler pressure.

  • Turn off your boiler. Allow it to cool down.
  • Locate the external filling loop. This is usually a metal hose with a couple of valves attached to it (one at each end).
  • If you can’t find a filling loop, look for a keyed filling loop or keyless internal filling loop.
  • Turn on the valves on your filling loop. This will allow water from the mains to flow into the heating system. As water flows into your boiler, your boiler pressure will go up.
  • Monitor the pressure gauge. Wait till the pressure reaches one bar and then shut off both valves. Be careful not to over-pressurize your boiler.
  • Release the filling loop. Some water will come out of the loop. This is perfectly normal. If water keeps running, tighten the valves.
  • If you removed any end caps from your boiler pipe, replace them.
  • If there are no leaking water signs and the pressure does not drop, switch on your boiler.
  • Once the boiler cools down, check the pressure gauge to see if the pressure has dropped significantly.

If your boiler pressure drops more than twice a year, check your pipes for signs of leaks. Green deposits near joints in copper pipework or stains on the ceilings or skirting boards could indicate a problem. If you find a water leak or your boiler pressure keeps dropping significantly, schedule a boiler inspection.

High Boiler Pressure

If your boiler pressure gauge reads 2.5 bar or over, you have high boiler pressure. There are several reasons why boiler pressure increases. You could have accidentally put more water in your system than recommended or left the filling valves open, or not screwed them tight enough.

How to Decrease Boiler Pressure?

Here are steps to decreasing boiler pressure

  • Turn off your boiler.
  • Make sure the filling loop valves or the key or keyless filler are fully closed.
  • Allow the system to cool. Bleed the radiators. If you haven’t bled your radiators before or hit a roadblock, get professional help.
  • Once you have bled all your radiators, check the pressure gauge. If you are still getting a high reading, repeat the bleeding process.
  • Do not stop until the boiler pressure is between 1 and 1.2 bars.
  • If you accidentally reduce your boiler pressure too much, repressurize your boiler. Once your boiler pressure normalizes, remember to shut off the filter valves.

If your boiler pressure keeps rising abnormally, have your contractor inspect your boiler.

John Owens Services Inc. offers top-notch VAC repair services near Novato. Our heating and cooling experts know everything there is to know about HVAC systems. We will help you select the right HVAC system size for your home as per your heating and cooling requirements. To schedule an inspection, call 707-207-8592.

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San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464



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San Rafael
(415) 942-6565
Santa Rosa
(707) 452-3464