pressure dropping with combi boiler

[BrianRHobbs]

Hi Guys,

I'm hoping someone can give me some advice regarding my combi boiler. Recently it's been losing pressure (dropping down to zero). When this happens, I top it up to about 1-1.5 bar but over the course of 1-2 weeks, it drops back down to zero.

I've searched the forums before regarding this & have seen 2 possible causes for this:

1. a leak in a pipe
2. a dodgy pressure release valve

without taking the carpet up, it's hard to check the pipes, so I've been keeping an eye on the outlet pipe. Here's what I've seen:

at about 2 bar, there are occasional drips at about 3 bar, there are constant drips at just over 3 bar, there's a constant trickle

I've got 2 questions I thought I'd ask before getting a plumber out:

1. are these pressures normal/typical?
2. should I be getting the drips / trickles at those pressures?

thanks in advance, Brian

[Newshound]

I think you have found your problem. Although there might not be much space around the valve, if you are reasonably confident with spanners they are usually not too hard to replace. About a fiver from BES, make sure you get one with the same pressure rating and the same fittings, they are usually

3/4 BSP but all combinations of male and female. What kills them is if they lift from overpressure, or if you manually open them with the plastic knob because you have taken the pressure a bit too high. When they lift, a bit of debris often gets stuck between the faces and then the seats corrode / erode until you get the symptoms you are seeing.

[gasman pete]

Hi Brian, Reading your post you said there was a drip at two bar upto a trickle at three bar..... does the pressure go from one bar cold to three bar hot? or how high does it go? what boiler is it ? it sounds like the saftey valve has failed .. but why ? maybee it has another fault that causes the pressure to keep rising. that is why i need to know how high the pressure goes from cold. regards pete

[Jason]

This started happening to me, and it turned out the expansion tank had lost all its air. Getting that pumped up again did the trick - the leaks have stopped, the pressure now holds without topping up. See if you can find the post from about a week ago (it was an Ideal 120 boiler). It is worthwhile checking at least. Without that room for expansion, the pressure builds up extremely fast and opens up leaks and safetly valves that would normally hold.

-- JJ

[Lurch]

On 26 Feb 2007 12:30:30 -0800, [e-mail] mused:

No, you shouldn't be hitting 3 bar.

Yes, if the PRV is a 3 bar one (should say on the cap in the boiler) then it is doing what it should. I'd be more concerned as to why it gets to 3 bar rather than 0 bar.

[Ed Sirett]

See FAQ.

[Simon Stroud]

My Eco Hometec-badged Man Micromat combi did this a few weeks ago. The diverter valve failed and we had to call them out to fix it. £339 Eeek of which £210 was the valve. Double Eeek!

Anyway the repair man drained the boiler by using the knob on the "Duco" pressure relief valve and this leaked slightly as soon as he went away.

In the Micromat this valve has a flexible clear plastic hose that runs to the condensate drain. I removed this hose so I could see what the valve was up to and sure enough there was a small but persistent drip and I was losing pressure over about 2 days.

I was going to call them back but managed to fix it instead. I just turned the knob to let out a LOT of water at a big flow rate and this must have cleared the crud because it now seals properly.

Anyway, might be worth a look.

Regards, Simon.

[Unclebill]

I have been reading this thread with interest as I have a very mino problem with my Euro Combi SX 20. Due to its placement it is almost impossible to view under the boile with BOTH eyes at the same time! making distance judging tricky ! I am a complete amateur at any sort of plumbing so all I can do is tr to describe what I can see. Supply, flow and return and gas pipes all run vertically into th boiler against the wall but there is one pipe approx 1/2" in diamete with a red valve on it which runs horizontally in front of the vertica pipes, on the end of this pipe next to the valve is either a corrugate hose outlet of approx 1/4" dia, or its a tapered threaded end - wit only one eye its hard to tell ! For the last week or so a minimal dri has formed at this end of the pipe (perhaps a table spoon of clea water per week.) Can someone suggest how I can stop this drip, its not exactly lif threatening but it is irritating as it drips on the worktop

-- Unclebill