What should I do if my boiler loses pressure?

February 1, 2020

If you've got a boiler losing pressure, then it's important that you check every possible issue before trying to fix the problem.

Whats in this article?

• Possible causes
• Is low boiler pressure dangerous?
• Why is it losing pressure?
• What should the pressure be?
• How to top-up pressure
• Still not working?
• Boiler error codes for losing pressure

Identifying the cause is almost as important as noticing the low-pressure boiler in the first place, especially when it comes to deciding if you need to contact an engineer for advice.

What causes a boiler to lose pressure?

Low boiler pressure can be caused by two major problems, both of which occur in different ways. The first involves a water leak somewhere in the pipework: if left unchecked and unidentified, a leak can reduce the overall pressure of the water, as well as wear down the pipe and let extra air into the system. In worst-case scenarios, this might even result in a pipe starting to wear down faster, making the leaks bigger and causing more water to be wasted. This could even flow down onto other parts of the system or unrelated areas of your home, damaging key parts of your radiators or central heating system.

The other common cause of pressure loss is with the boiler itself. If there are no leaks and none of the other appliances are faulty, then your boiler may simply be too old, broken or damaged to move water through a certain pipe properly. Thankfully, there are ways to fix this, but it varies depending on the sort of boilers you have installed.

Is low boiler pressure dangerous?

Low pressure, on its own, won't usually be dangerous, unlike high pressure. However, if your boiler suddenly loses pressure at a rapid rate, it could be a sign that water is leaking out somewhere in your home. This leak might damage electronics or break important appliances, and not having hot water can make it difficult to stay warm in cold weather. Even if you aren't in any danger, you'll need to pay for more fuel to get the same amount of heat, no matter how good your radiators may be.

Why is my central heating boiler losing pressure?

Central heating is one of the most important uses of a boiler in any home. Many people in the UK use a combi boiler, due to them being the cheapest and most accessible option - this generally means that it will be connected directly to the house's heating. If you spot low pressure on boiler readings, you can expect the heating to get less efficient almost immediately.

If your pressure gauge doesn't find your boiler pressure low, then it's likely happening somewhere further in the system. A leak in pipes further in the system, past the boiler, won't appear on your pressure gauge, since it only checks a small section of your entire system. If this is happening, the issue isn't with the boiler, and might actually be with a radiator (or multiple radiators) elsewhere in the house.

What should the pressure be on a boiler?

Different boiler models have different limits, but most boilers are designed to be around 1 and 2 bar units. If it's too high, you can use a pressure relief valve to try and reduce it, but you can't do the same with boiler low-pressure issues. It might simply be a case of adjusting a certain valve to let more water through, filling the main pipe and increasing the amount of force it's putting on the system.

Always check your manual before you make an adjustment like this. Taking the pressure too high or low, even for a second, can waste fuel and might end up with you losing control entirely. If you leave it as an excessive amount for too long, you could even end up destroying a large part of your heating system, especially if the boiler relies on the constant movement of water to function properly.

How to top-up (repressurise) your boiler

Restoring the pressure to your boiler isn't usually that tricky, and you don't need to call out an engineer unless it starts leaking or a valve becomes too faulty to use anymore. As mentioned earlier, the pressure is generally directly related to the amount of water filling the system, which is why a leak will reduce it so much. The less air you have filling a radiator, the more efficient its heating will be.

First of all, make sure you check the manual to get important deals about each valve, as well as figure out if you're using a combi boiler or not. Switch your boiler off completely, and then attach a filling loop from the mains. Open both major valves so that water can start leaking in - you're essentially flooding the system with water directly. Once you reach your desired pressure (around 1.5 bar, in most cases), close the valves and turn the boiler back on, resetting it if necessary.

Boiler keeps losing pressure, even after being repressurised?

If the top-up didn't' fix your boiler pressure, something else is causing the pressure to leak out of the system instead. The more you're losing, the bigger the air or water leak, so you'll need to track it down quickly. These issues might include:

• Water leaking out of some pipework in a key spot (repair or replace the pipe).
• A pressure relief valve that's been left open (find and close it).
• Bled radiators that have released air into the system (stop the bleeding, then wait a while for the pressure to flatten out).
• Not enough water coming into the system (check to see if the mains are flowing into the system correctly).
• The boiler is broken. In some cases, your entire system is just too worn out to keep working - this only really happens if you've had the same appliance for many years without proper maintenance or replacement parts, in that case you will need a new boiler.

Error codes for losing boiler pressure

Certain electronic boiler models use error codes to tell you about major problems, such as a leak or sudden increase in the amount of air in the system. Using these codes can help you track down problems before they become more significant, and might even help you fix the system before it puts itself into a lockdown or shutdown mode.

Keep in mind that not all codes will apply to all boiler models, and some of them might only appear under certain circumstances. Always look in your manual for this documentation so that you don't make a mistake and try to solve the wrong problem.

Viessman Boiler Codes:

• Fault Code C1 = Differential air pressure.
• Fault Codes B9, ED, F0, F-E5, F-EC, F-ED, F-EE, F-EF, F-FD, F-FF = Maximum pressure limiter issue.
• Fault Code F5 = Faulty gas pressure switch.
• Fault Codes EE and EF = Faulty air pressure switch.
• Fault Code 0F = Service required.

Alpha Boiler Codes:

• Fault Code 1 = General ignition failure.
• Fault Code 2 = Low pressure in the primary system.
• Fault Code 61 = Incorrect system pressure, air in the pump.
• Fault Code 0A37 = Insufficient pressure and flow (switches the boiler off automatically).
• Fault Code 0E37 - Insufficient system pressure.

Worcester Boiler Codes:

• Fault Code E9 = Safety limiter.
• Fault Code A1 = Dry pump.
• Fault Code F0 = Major internal error.
• Fault Code CE 207 = Low water pressure.
• Fault Code H07 = Low water pressure that is impacting performance.
• Fault Code 1065 B = Pressure sensor is defective.
• Fault Code 1970 B = Sudden, rapid drop in pressure.