Pressure drop in Worcester Combi Boiler

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Pressure drop in Worcester Combi Boiler

Postby rbritt » Wed Oct 11, 2017 11:59 am

Hi all. I'm having a problem with either my Worcestor combi boiler or central heating pipes where the pressure is dropping. I'm hoping people can give me some help to determin where the fault is.

At the start of the year it was a very slow drop and an occasional topup was enough.

This might not be relevant but around that time I started to notice a 'water hammer' sound when turning off our either our hot or cold taps. I read this could be do to air chambers in the pipes losing their air so I drained the water from the taps and refilled it, that would fix it for maybe a week but it would come back. Doesn't seem anywhere near as bad these days though :/

Now the heating is back on and when we get a much quicker drop of pressure in the boiler. One day I recorded 1.3 bar over 6 hrs 20 min.
Overnight when the heating is off I recorded a 0.5 bar drop of pressure (about 9hrs), though this varies.

I've tried to do a couple of tests to see if it's the boiler. I topped it up, hung a bag on the overflow/blowout pipe outside to catch any water from that but after the pressure dropped to maybe 0.2 bar there was not a drop in the bag.

I haven't checked the condensate pipe - could that be something to do?

I did another test last night. I topped the boiler up to 1.5 bar and turned it off. Then a closed the central heating isolator valves under the boiler (I didn't touch the cold/hot water pipes). In the morning the boiler pressure read about 0.8/0.9 bar.

When I reopened the valves this morning I could hear a flow of water for a moment but the pressure reading on the boiler barely moved.

A friend pointed out that when I topped up the boiler the water could still have been warm and as it cooled the pressure could have dropped... so maybe a bad test.


So that's everything I can think of at the moment. What do you guys think? Boiler problem or a central heating leak? Any help is greatly appreciated!
rbritt
 
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Pressure drop in Worcester Combi Boiler

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Re: Pressure drop in Worcester Combi Boiler

Postby kfordgas » Wed Oct 11, 2017 2:41 pm

Hello and a warm welcome to the forum
It sounds like you have an internal leak on the heat exchanger. When you opened the flow and return isolation valves, had the leak have been on the system it would have dropped to 0 bar pressure when you turned them open.
Thanks
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Re: Pressure drop in Worcester Combi Boiler

Postby rbritt » Sun Oct 29, 2017 5:39 pm

Hi, thanks for the reply kfordgas and tip about the heat exchanger. I like to understand how things work as well as I can (not so I can fix it myself in this case but just because I like to know what's going on!) so I read into heat exchanger problems a bit.
I found this page which seems to explain different problems nicely:
http://www.lovekin.net/plate-heat-exchanger-faults.html

With a leak in a heat exchanger it seems there should be leaking water going through the 'safety pressure release pipe' that goes outside? When I had a bag over this pipe I didn't collect any water though :? The page also seems to say that the pressure would raise as the higher pressure mains water would be pushing though the heat exchanger leak? Don't mean to second guess anything, just trying to understand what's going on!

Cheers
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Re: Pressure drop in Worcester Combi Boiler

Postby kfordgas » Wed Nov 01, 2017 9:36 am

It is an internal leak which drains away via the condensate pipe and one which is difficult to see, but van be proven by isolating and elimination.
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Re: Pressure drop in Worcester Combi Boiler

Postby rbritt » Sun Nov 05, 2017 4:17 pm

Looks like you're right to me! I setup a bucket to catch water from the condensate pipe and put a webcam to record it on timelapse with the boiler pressure needle visible.

https://www.youtube.com/watch?v=-uow5owWftY&feature=youtu.be

You can see just how much water came through that pipe in 25 minutes before the pressure went to near zero from 1.5 bar. Looks like new boiler it is.
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