Ferroli Demicondens 26 c losing pressure

[Paulplumb]

Hi all, I need to pick your brains! I don't do many boiler repairs and would some advice please.

I visited a customer the other week to replace a radiator. She had only just moved in to the property and she was advised by the former owner that every few weeks she would need to top up her combi boiler with water (Ferroli Demicondens 26 c) . I showed her how to do this and explained there could be be several reasons for the pressure loss. I checked all pipe work in the loft for mouse nibbles as it is all 10mm speedfit pipe. I checked all rad valves and ceilings for signs of leaks (None) . I dropped the pressure from the system and topped up the pressure vessel as it was low to empty. The PRV is right next to the front door and there are no signs of it having leaked and the customer has never seen it discharge water. When the boiler is running the heating full chat the pressure slowly increases to 2 bar and holds. Apparently now she is having to top up the system every day or so. It is not my rad pipe work leaking (I checked!). I am now thinking the next course of action is to recheck expansion vessel and if that is sound then top the system back up and isolate the boiler at power and flow and return and run the condensate pipe in to a bucket and check for a pressure drop/water in bucket. Would you all concur?

Thanks in advance

 

[Ermintrude]

Are you a gas engineer ?

 

[Dotty]

Are you a gas engineer ?

Yep, he is. This is in the private forum, tapatalk boy.......

 

[julesverne]

Could be the secondary heat hex as im surethey are aluminium can be prone to getting a hairline that when it cools down.
Or you charging up expansion vessel has made a pin hole in diaphram bigger so needs topping up constantly
or when drain system down a loose push fit is now even looser and peeing even more

 

[Paulplumb]

Thanks Jules. You have given me a couple of ideas

 

[julesverne]

Keep us posted.

 

[ambrosia]

you need to do more to locate the area the leak is in 1st

under the boiler should be a valves for the flow and return. after the boiler has been topped up close both flow and return and leave for a week, the customer will still have hot water in the mean time

after a week if the pressure is still okay at the boiler you know its somewhere in the carcass
if the pressure has dropped then youre looking at the boiler

unless of course the valves are letting by, then youre screwed

 

[Paulplumb]

Thanks Ambrosia. I don't think I will have to wait a week to see a drop in pressure. She says she is topping it up daily Went there first thing this morning. I really don't think there is a leak on the heating system itself. I have a suspicion that it is the secondary heat exchanger as Jules suggested. I checked vessel pressure after dropping the system pressure and it was spot on. I then repressurised the system but isolated f&r, cold in and capped off the hot out (no isolator on hot). I am pretty sure when i the go back in the morning the system will still be at 1 bar. If that is the case i will then reconnect the hot, leave the f&r closed but ask the customer to run the hot tap periodically to simulate normal use. I am thinking the pressure will drop then as the secondary heat exchanger lets by.

At least that's theory!

 

[ambrosia]

turn the boiler off and let it cool for a short while, pull out condence pipe, top the pressure up and see if any cold water comes out, leave a glass under if its really slow while you have a cup of tea and have the customer tell you all about her holidays, best if youre on an hourly rate.

have a close look at where the flow and return connect to the heat exchanger, those joints can be dodgy

also if you do what i recommended in my previous post and youve proved its not the carcass, then you know its the boiler and if you get stuck you can just make up a load of rubbish tell the customer boiler is beyond repair and she needs a new one (its a get out of jail all boiler engineers use when theyre stuck even if they wont admit it)