Boiler Pressure problems

Your expansion vessel has lost its pressure

What a boiler technician might say; “Your expansion vessel has lost its pressure.” What they mean: Expansion vessels are found in most boilers, especially combi boilers, and are needed to cope with the extra water created by expansion during the heating process. Expansion vessels work at pressure. If this pressure is lost, the expansion vessel cannot do its job and the boiler will fail to start or will automatically shut down.

An installer can usually tell if the expansion vessel has failed as the boiler pressure gauge will show a great increase of pressure as the boiler heats up. A faulty expansion vessel will not always need replacing – often it will simply need repressurising. Your installer will be able to tell you the most cost-effective way to fix the problem. They may recommend replacing the external expansion vessel but this can be more expensive.

Your PRV is dripping

PRV is short for ‘Pressure Release Valve. This is a safety device, built into a boiler that activates if the water pressure rises to a level the boiler cannot cope with. The PRV switches the flow of water to a pipe that usually discharges outside of the house. The PRV is a key safety feature of the boiler.

If you see any dripping from the PRV or discharge pipe you should contact your installer. Often they may simply have to recharge the expansion vessel. The PRV should reset and any dripping should stop once pressure returns to normal levels, but sometimes the PRV will continue to let water drip from the system. When this happens, the valve may need replacing.

You have poor flow rate from your taps

Flow rate is the term to describe the rate at which water comes out of your taps or shower. A poor flow rate means that the flow of water from some or all of your taps or shower, will be low. You can measure flow rate in litres per minute. An installer may calculate this by timing how long it takes to fill a measuring jug from a tap. Flow rate problems are typically found in open-vent systems. These systems rely on gravity to push water from a storage tank to taps and showers. The greater the vertical distance between the taps and the tanks in your loft, the better the flow rate will be. If the tank is too close to the outlet, the flow rate may be poor.

A combi boiler won’t meet your hot-water demands

A combi boiler will not be able to produce all the hot water you need. This means you will not get enough hot water out of all of your taps at the same time. You would be better suited to a system with a hot-water cylinder. Combi boilers are not necessarily suitable for every home.

If you have more than one bathroom or a large family who all need hot water at the same time, you should bear this in mind.


Boiler Pressure Problems? Here’s What to Do

Combination or Combi boilers were invented in the mid-1800s, but it was only until the 1960s that boilers started being used for domestic heating purposes. In the 1980s, the combi boiler went through some major changes, involving the use of a filling loop that gave us pressurized water in the central heating system. One of the most common problems with a combi boiler is that it sometimes loses its pressure.

Combi Boiler Losing Pressure

Once you find that there is a decrease in the pressure of your combi boiler, the first thing you should check is for any visible leaks. A good place to start would be the pressure release pipe that goes from the boiler system to the outside. If you are unable to locate the leak, then it is best to contact a plumber. If you do find the leak, you should never place a cap on it as that would make it a health hazard, dangerous for you and your family.

A boiler losing pressure could also be due to wear and tear. Pressure loss in boilers can also be due to air in the radiators. If the boiler system you are using is more than 20 years old,then it is likely that the leak is at the expansion vessel or the auto air vent. Water leaking from the pipe is often sign of a fault within the expansion vessel. If you find a leak in your boiler system it is important to call a Gas Safe Plumber and not attempt to make any fixes by yourself, unless you are a plumber (Gas Safe).

Re-Pressuring Your Boiler

A boiler not working is often due to a loss of pressure. This can be checked by the water pressure indicator that’s placed at the front of a boiler, which should always be showing one or two bars and is an indicator of atmospheric pressure. You can increase the pressure of your boiler by locating the filling loop, which is a silver/greycoloured pipe with a valve at both ends. This is normally located under the boiler. You will need to do the following to re-pressurize the boiler;

  • First, make sure the boiler has been switched off, and it’s not hot
  • Make sure the ends of the hose are attached to the valves
  • Use tap handles or flat headed screwdrivers to open the valves
  • Now, open both the valves and allow the cold mains water to go into the boiler system
  • You should be able to hear water filling in the system
  • While the water is filling, keep an eye on the pressure gauge. When it reaches 1.5 bars close both the valves at either side one after the other. The boiler’s pressure should return to normal.

Bleeding Your Boiler

You may also need to bleed your boiler to return the pressure back to normal. Bleeding your boiler helps release any air trapped in the pipes. To bleed the boiler, do the following:

  • Use a small crescent wrench or pliers to loosen the bleed screw slightly. You will hear some hissing sound which is an indicator of air being released
  • Push the reset button on the furnace to turn it back on
  • Now, tighten the screw as soon as the air stops sputtering out and a steady stream of fuel pours out.

Quick Discovery