Boiler Pressure drops to nil when the heater is used

JackeeBoy

Hi all

Just wondering what the problem may be. I have recently started using the heater and noticed when I have it on for a few hours during the day, the next morning the pressured has dropped all the way down I have to top it up again. Just wondering what the issue could be and how I can go about diagnosing it?

akira181

You haven't said what kind of heating system you have so I'm assuming it's a combi boiler. If there are no leaks on your system then it's likely the expansion vessel does not have enough air in it or there is a blockage to the vessel. If there is no air in the expansion vessel, you'll be losing water through the pressure relief valve whenever the heating is on as water does not compress easily.

A simple test would be to fill the system to 1.5 bar when cold. Turn it on and check the pressure gauge 10 minutes later. The pressure gauge should not move, if it goes up then it's the expansion vessel. It's an easy job to pump the vessel back up (can be done with a bike/foot pump, what pressure depends on the make and model of the boiler) and is something that should be checked during an annual boiler service. As always with gas appliances, get a professional to do it if you don't have the experience to do it yourself.

JackeeBoy

akira181 wrote: »

You haven't said what kind of heating system you have so I'm assuming it's a combi boiler. If there are no leaks on your system then it's likely the expansion vessel does not have enough air in it or there is a blockage to the vessel. If there is no air in the expansion vessel, you'll be losing water through the pressure relief valve whenever the heating is on as water does not compress easily.

A simple test would be to fill the system to 1.5 bar when cold. Turn it on and check the pressure gauge 10 minutes later. The pressure gauge should not move, if it goes up then it's the expansion vessel. It's an easy job to pump the vessel back up (can be done with a bike/foot pump, what pressure depends on the make and model of the boiler) and is something that should be checked during an annual boiler service. As always with gas appliances, get a professional to do it if you don't have the experience to do it yourself.

Thanks. Yes, it's a combi boiler and when I fill it back up to 1.5 and turn the heating on, the pressure does go up. No idea how to do what you just suggested so will hire someone unless it's something I am allowed to do myself?

Ectophile

I would expect the pressure gauge to go up a bit as the heating warms up. That's totally normal. Maybe an extra 0.5 bar, though that depends on your system, and the temperature you have set.


If it shoots up to about 3 bar, then assume the pressure vessel has failed. It mat be possible to re-pressurise it, or it may need a new vessel.