pressure drop on boiler

24 Mar 2012
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United Kingdom
Hi, the pressure gauge on my boiler keeps dropping slowly overnight from 1 bar, with the temp gauge turned down to zero in the hallway. I turned all the rads off and increased the boiler pressure to 2 bar which I left overnight, again with the central heating gauge turned to zero in the hallway. with no drop in pressure the following morning. I reduced the boiler pressure back to 1 bar, and began opening one rad at a time nightly, again with the hall temp gauge on zero. my question, -- is there a way I can test for this pressure drop other than what I am trying?, as there are 16 rads, and I am unsure doing what I am will locate any leak etc`. I have tightened all fixtures and fittings with no water leak visible, is there an alternative way I can pressure test the system, the pressure drop only seems to occur when the temp gauge in the hallway is asking the boiler to heat the rads, is there a simpler solution ???. The boiler is a Worcester greenstar 30cdi, feeding a OSO unvented system, which incorporates both the domestic & Central heating system, Grateful for any constructive advise, Goafer.
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Might be discharging through the pressure relief valve to outside when the system heats up.
Put the heating on and watch the pressure gauge till the system is warm. It should rise only slightly, check the discharge pipe outside (usually 15mm copper not to be confused with a condensing boiler discharge which is normally plastic and larger) for escaping water it may be your pressure valve faulty. If it rises rapidly to around 3 bar and lets the pressure go suddenly by discharging hot water (keep well clear of the discharge pipe!) to outside chances are your pressure vessel is shot, a job for a qualified engineer either way but at least you will know how the water is escaping.

Best wishes,
Hi Footprints. many thanks for your advice which I tried, turned the C/H on as suggested, which fired the boiler, which began plooming, once the rads that I had opened began to get warm, I checked the pressure gauge on the boiler which had risen slightly, I then checked the outside 15mm copper pipe with no sign of any water present. The boiler continued to flame and the pressure gauge increased marginally over the 1 Bar, the digital display counter was reading 56, by this time time the rads were getting hot. As there was no apparent fault, I turned the system to auto once more. What I really would like to know, is there a way I can pressure test the radiators when all are closed/opened, without switching the system on. My thoughts are if I could do this at a significantly higher pressure, any leak no matter how trivial might show itself, or even slightly drain a rad`, and put some kind of dye or the like in the rad, which may eventually show itself should there be a leak as I suspect. My thoughts behind this logic are, if there is a very minute leak which ocurrs when the radiators are on, the heat may well evaporate any water without trace. Goafer.
Before you go to bed tonite pressurise the system and close the valves on flow and return to boiler.
If in the morning the pressure is still there then the leak is on your system somewhere. (deal with that after wards)
If the pressure is gone you know the fault is with the boiler, most likely the prv.

When was your boiler last serviced?
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Hi goafer,
Sorry I couldn't help, as you say it's not unheard of for one or several small leaks to vaporise on a hot pipe and not show up as drips.

The only way they can be spotted usually is that after a time they tend to leave traces of scale or verdigris on the pipe. Common places are radiator connections and around the spindle of rad valves under the plastic cap.
Most plumbers rely on the MK1 eyeball or running a dry finger around suspect pipes and checking for moisture that way.

It is feasible to pressure test pipework but few plumbers will have the equipment but that will only confirm what you know, that it's leaking and it still relies on spotting the leak. Drains can be tested with dyes but it's not intended for CH systems. Apart from anything else imagine a leak of dyed water getting on a carpet and how hard it would be to get all traces out of the system.

Only suggestions are, isolate just one rad at a time and try it for a day. I know you have turned them off but did you close both ends of the radiator? One end is the customer control the other is set by the installer if you turn this one off make a note of how many turns are required to close it so you can set it back to the same flow when you turn back on.

On balance I would suggest calling a qualified installer who with experience may be able to drop straight on the problem and sort it out simply, who knows, it may be a known problem with your boiler or another component of the system that he will be well aware of.
It's worth a call out fee if it solves the problem as even when you find the leak, you will need a Gas Safe fitter anyway if it turns out to be related to the boiler might as well tie it up with a service if it hasn't been done for a year or so.

Best wishes,
Many thnx to both Gasservice1985, & footprints, I will certainly try what has been suggested. When you say pressurise the system, to what 1, or 2, Bar,, or more ?. Yes I did isolate both ends of the radiators, and did make note of how many revolutions I turned when closing the locknut. You would have thought in this day of technology, someone would have devised a means of pressure testing for leaks on radiators which I am certain is an everyday occurrence, a device whereby you blank the end of the return pipe on the last radiator, and connect a pressure system with gauge to the start of the flow pipe on the first radiator. which I guess to all intents and purposes is what Gasservice 1985 is suggesting, albeit from the boiler, however were this intended surely the boiler manufacturers should incorporate this in their manual and thereby make things easier. Seems archaic to me to have to improvise in order to hopefully obtain a solution. Still I live in hope of finding my leak, if not this year, then !!!!!!!!!!!!. I will keep you informed of any outcome, Goafer.
Pressurise as normal around 1bar

If the pressure is still there in the morning but drops when you open the valves back up the leak is on the system.
Sorry I obviously misread your original post. That the pressure remains with all the rads isolated?

Are any of your rads older than others ?

Bare with me on this cos it sounds stupid
Roll out toilet roll along the length of the rads underneath and pressurise to around 2bar.

This will show up the smallest of drips.

Also use a mirror to look for signs of rust/corrosion on the back/bottom of rads.

When refilling a system once I noticed a tiny pinhole on a rad when I rad my finger along the bottom of the rad it fell to pieces in my hands and made a bit of a mess
In response to both footprints, and gasservice 1985, this is where I stand at present, last night pressurised the boiler to 1 Bar, having previously opened 7, of the 16 Rads, Turned down the temp`gauge in the hallway to zero, that was around 23 15 hrs, left the boiler on, got up @10-00am, checked the boiler which had held the pressure @ 1 Bar. Of the 9 rads remaining I will open 1 at a time which if the pressure drops should indicate which, if, any radiator is leaking?. I will of course re-pressurise the boiler as I go along.

Having previously turned off all the rads`and pressurised the system to 2 Bar and left overnight I am reasonably certain any leak is not on the on the flow and return pipework servicing each radiator. Although this was done with the Temp gauge turned to zero, therefor the boiler isolated from providing hot water.

Having said that, does the system need to be operational, IE, boiler working and heating any open radiator, or, is it the same if the boiler is off and the system just pressurised to 1 Bar when cold?. My thought being maybe any leak would only ocurr if the pipe work expands when hot!!!!!!!!!. the obvious answer is test it both ways, consequentialy I could be drawing my pension before the problem is solved.

To clarify, the boiler is less than 18 months old and was serviced 6 months ago, All the rads were installed at the same time 20 yrs ago. The system runs off 10mm micro bore
Should make little difference if it's hot or cold, but I would heat the system as that's the way it normally runs and there is just the slight chance that expansion is having an effect.

Why not do two rads at a time to speed things up when you get a drop try one or the other to confirm which is at fault, assuming you only have one leak that is of course :)

Good luck,

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