Worcester Bosch 30CDi Faulty?

[Crinkmeister]

I had a 30CDi installed a year ago as a replacement for a conventional system. All the rads were left, but each fitted with TRVs. After a month or so, I noticed one of the rads was rusted through at the back and as they were all 20 or so years old, I replaced them all one by one over a couple of months. Each time, I re-pressurised the system, re-bleeding as necessary and all seemed fine. When I got the annual gas safety check done a month or so ago, the engineer said that he had to top-up the system as the pressure had dropped slightly. I have to do this now about once a week. There are no leaks anywhere and I cannot see any discharge from the pressure relief pipe. I can always get a small amount of air from the upstairs rads after which the pressure drops to near zero. The system was filled with inhibitor on installation and I have added more (via the Magnaclean) after replacing the last rad. Upstairs rads (5) are plumbed in 15mm, downstairs (3 rads) are all in 8mm. Is there any fault possible with the boiler that could result in a pressure loss while allowing air into the system? I am not asking for DIY advice as it's a rented house (my son and family actually, so subsidised rent!), but I wonder if I need to go back to Worcester Bosch? The system works fine most of the time, I just don't understand where the water goes unless it's down the condensate pipe (difficult to check) and how air gets into a pressurised system.

Thanks for reading!!

 

[lame plumber]

every time you pump in fresh water you cause more corrosion, it takes a while for things to settle even with inhibitor in it, so fill it, leave it for 2 - 3 months then have a look if its still dropping. probably its a dodgy rad or valve, wb will not be to blame for this one tho.

 

[Crinkmeister]

Thanks for quick reply! - I did wonder about having to keep adding fresh water and I guess the "air" might be hydrogen, but if I'm losing water where the "bleep" is it going?! Nothing is soggy or damp anywhere - yet!!

 

[dancinplumba]

could be under ground floor where its not seen or as lame says a rad valve or the tappings at the top of rads. check around when system is cold as they dry up with the heat off the system

 

[Crinkmeister]

Thanks dancinplumba, It's a solid floor and pipes for downstairs rads drop down the wall - again no obvious damp anywhere. It doesn't actually need to lose much water for pressure to drop half a bar does it?

 

[dancinplumba]

no very little just have a good look round rads etc when its cold try using a bit of tissue to touch things and see if it gets wet. take off plastic valve covers if you can, if there is any green stuff,this could be where your leaks are

 

[Crinkmeister]

I'll do that - thanks again!!

 

[DirksPlumbing]

I'll do that - thanks again!!

Expansion vessel has been checked correctly? I feel stupid asking this again and again and again.
But this week I had 3 already, last week only 2.

 

[Crinkmeister]

Thanks Dirksplumbing. When I had the safety check done, I wasn't actually present, but the engineer did check the boiler and said it was all ok. What would be the symptoms of a failed expansion vessel - too much pressure? I'll check your other posts!

 

[Roger Welton]

Failed expansion vessel = pressure rises substatially when the heating is on

 

[Crinkmeister]

Think I have found the leak!!...Just topped boiler up again and went to bleed rads. Started with bathroom rad - always get a little air out of this one but very little if any from the others - maybe a clue? Although it all looked dry round the valves, and top plugs, I removed the plastic pipe covers for a closer look. Telltale greeny-blue deposit at the back of the pipe and a hint of moistore on the inside of the pipe cover. Nipped up the compression joint a little and fingers now crossed for now more dropped pressure.

 

[DirksPlumbing]

Good luck with your pressure loss. The slight leak would at least have been contributing. But as for your suspicion that the air in the radiator would give a hint where to look for the leak this is rather wrong.

Unless you have a negative pressure system ( pump on return, low header tank and large pipe resistances).

 

[Crinkmeister]

Seems to be holding up so far. I noticed a tiny weep on one of the Magnaclean couplings as well, so next time I'm round there with a spanner, will give that a tweak too.

I thought that about the negative pressure, but it's a combi, so I don't really see how air could get sucked in. But as lame plumber said, filling with fresh water will also introduce air. Maybe the air was trapped in an unused pipe somewhere - there is one capped off in the kitchen, but it's an 8mm and it disappears into the wall, so I don't want to touch that.

I'm grateful to all those who replied.:yes: