Vaillant Boiler - Losing Pressure

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Hi,

I wondered if I might be able to get a bit of advice before calling in a heating/boiler engineer. Apologies for what might be a long post but I wanted to try and give as much detail as possible.

We have a Vaillant EcoTec Combi-boiler which has been losing pressure recently, around 0.1 bar every other day.

I haven’t ruled out a leak in the system yet but I have checked around radiators which seem fine and there is no evidence on the ceiling as of yet to a leak upstairs. Admittedly I haven’t lifted any floorboards yet or checked any hidden pipework.

The reason I’m not convinced there is a leak in the system is that we have had no issues with pressure for the last three years since we moved in. The issues have only started over the last 3 weeks since we had a new bathroom installed. Obviously it could be coincidence that a leak has occurred in this time but it seems more likely to coincide with the plumbing work that we have had done.

We had an old heated towel rail in the bathroom which was replaced with a new one during the refurb. I posted on here recently and mentioned that the plumber had left the boiler over-pressurised, I noticed it was at 2.8 bar when hot (2.2 when cold) one night after work. I bled some rads off and managed to bring the system down to 1.5 bar when cold.

Last weekend I noticed the towel rail needed bleeding already, I bled this off as well as another rad in our spare bedroom which was also cold at the top. I noticed the boiler pressure was at 0.8 bar, so it has obviously been dropping since I re-pressurised the system. I topped it back up to 1.5 bar on Saturday however it is now reading 1.3 bar when cold, so pressure is still being lost from somewhere.

When I filled the system up I noticed the plumber had unscrewed one of the filling taps and not put it back on, so I had to use a pair of pliers to turn the filling loop tap on as I can’t find the screw. Not the end of the world, but a bit careless on his behalf and coupled with him over-pressurising the boiler it makes me question if he may have done something else to the system.

Could it be that the PRV opened when the system was over-pressurised and has not reset itself, and is still letting small amounts of water out?

My other thinking was could the towel rail have been fitted incorrectly and is slowly letting air in to the system and affecting pressure? I wouldn’t have expected it to need bleeding just 2 weeks after being installed. With that being said though the towel rail was still piping hot this morning so it doesn’t appear that any air has got back in to it yet.

I read a post on here last year where a heating engineer mentioned systems can sometimes take time to settle down after being drained and re-pressurised, not sure if that is right or not?

Appreciate any help!
 

CBW

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  • Isolate the towel rail and see if pressure drops.
  • Check for water on the safety discharge pipe or Tie a bag around it and see if any water is present.
  • Could be unrelated to what work plumber has done, when’s the boiler due a service?
 
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  • Isolate the towel rail and see if pressure drops.
  • Check for water on the safety discharge pipe or Tie a bag around it and see if any water is present.
  • Could be unrelated to what work plumber has done, when’s the boiler due a service?

Thanks mate - I'll try isolating the towel rail for a couple of days and see if any difference in pressure.

With regards to the safety discharge pipe, would this be the pipe that water will come out of if the PRV is letting water through? If so, am I right in thinking this will be outside?

Service isn't due until later this year, I'm not ruling out a wider issue but all seems very coincidental with when the work was carried out.

Thanks for your help.
 

CBW

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Yes, the safety discharge is the copper pipe (usually) outside after the prv has operated.
 
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