Problem with sealed system.

[cr0ft]

Hi all.

Ok. In December I converted an open-vented system into a sealed combi-boiler heating system for a customer. I contracted a GSR engineer to do the boiler installation whilst I modified the pipework on the CH side of things.

The existing pipework was pressure tested to 5 bars for 30 minutes prior to connecting the boiler and there was no pressure drop. This was done with cold water obviously as the boiler wasn't connected (for obvious reason) at the time.

Since installation, the customer is now having to top the pressure up a couple of times a week. I have checked all visible pipework and radiator tails, there are no signs of leakage at all. PRV is not leaking. All the CH pipework runs above ground floor level through the usual arrangement of stud walls, solid walls and floor/ceiling voids. There are no signs of any leakage coming through walls and ceilings.

Given that the pressure is dropping from 1.5 bars to 1 bar every few days I would expect this to be a fairly big leak (if indeed water is leaking) and for it to be very noticeable by now in some way.

I've added 2 cans of Fernox F4 Leak Sealer via the filling loop today and will see what happens over the next couple of weeks.

I checked the radiators today and there are no signs of air in them. I also placed 2x AAR valves at the top of the system where the old open vent and overflow pipes were in the loft space. Due to the existing layout of the current heating system it was not possible to get easy access to the main flow/return pipework these teed off and cut them back there so this was the route I chose.

Does anyone have any other ideas if the leak sealer doesn't sort it out? Could the problem be the expansion vessel?

 

[aggis]

If you've double dosed the system with F4, I guess it's a big system , more tan 10 rads. Therefore it could be that you wil need another expansion vessel. Prob' going up to 3 bar when fully hot & relieving itself thro' prv.

 

[Alpha man]

Is there any pipe work running through concrete floors?

 

[rm1]

aggis has given you a good post the other issue you may have is a dead leg ie long run of pipe not doing anything that will gather air and cause a pressure loss

 

[SafeGasInstall]

I was told never ever auto air vents on sealed systems ....only manual ones !!!!

 

[yorkieplumber]

I was told never ever auto air vents on sealed systems ....only manual ones !!!!

well how come most combis have auto air vents then?

 

[yorkieplumber]

with it been an existing open vented system you may have very very minor leaks they are not always visible, ileak sealer should sort problem i would be suprised if it does not.

 

[SafeGasInstall]

well how come most combis have auto air vents then?

good point yorkieplumber ....I have been told when you run pipe work such as going to the loft and drooping down to feed radiators to the other said of the house to never have AAV in the loft ! me personally fit a thumb operated ones !!!

 

[SafeGasInstall]

If there is problem with the ev there will be water outside by the prv pipe

 

[mattyp]

What boiler is it ? Could be a faulty heat exhanger, the water would be running out of the condense pipe ? If it were me I would be isolating the flow and return under the boiler over night,( leave boiler off ) then go back to see if it had dropped. If it has you know the problem is on the boiler , if I hasn't dropped when you open the flow and return, if all of a sudden the pressure drops, you know it's on the system . Good luck !

 

[fuzzy]

I was told never ever auto air vents on sealed systems ....only manual ones !!!!

what reason?

 

[cr0ft]

Hi all and thanks for the post. It's a 12 rad system so also thought it may be that the boiler's expansion vessel isn't big enough. This said, there's no sign of water leaking from the PRV but that doesn't mean to say it isn't happening. I don't think there's any issue with AAVs on the tops of the old cold feed and open vent pipes. As I wasn't able to cut them out close to the flow and returns this was (imo) the best solution. If the system is working properly there shouldn't be much air in it anyway so air loss would be indicative of corrosion problems.

I've asked them to keep a log of pressures each morning over the next 2 weeks, realising that leak sealer can take up to 1 week to work. I think the next step after that is (as you say) isolate the boiler overnight and see if there is a pressure drop in the morning.

There is no pipework under concrete floors, all pipes are above ground floor level, all hidden in solid/stud walls and floor/ceiling voids. I would definitely expect to see some evidence of water leakage given the pressure drops (1.5 bars to 1 bar in 2 days). On a system this size, if it's a water leak, that's quite a lot of water.

I'm thinking if the leak sealer doesn't solve it the plan of action is: -

1.) Isolate boiler overnight to test boiler is water-tight the following morning.
2.) Check expansion vessel function.
3.) Bring in a leak detection specialist.

Anyone else got any better plans?

 

[cr0ft]

Oh and the boiler is a Broag Remaha 39C. Really good boiler (made by a division of Vaillant Group), we've fitted lots of them and never had a problem with any. Never say never though! rm1, there are 2 dead legs left on the system, both of which have the AAV valves on top of them (terminating in the loft space). These are the original cold feed and open vent pipes. They're run in Polypipe from the loft down to the 1st floor of the 3 floor house. I can't get to the flow/returns where they connect in without hacking out stud walls which the customer doesn't want for obvious reasons. This is why I terminated them with AAV valves.

 

[mattyp]

You could drain a radiator and leave it full of air, with one end open, this will act as a temporary expansion vessel . Run it for a few days, if the pressure is ok, you know you need to add a 2nd vessel .

 

[cr0ft]

I like that idea. Very clever Your always learning in this trade!

 

[mattyp]

Yep it's saved my life a few times !! Handy if you have a vessel fault also, as you can keep the boiler going by doing this until you fit a new one .

 

[fuzzy]

whats a leak detection specialist?

 

[cr0ft]

Can't advertise any of them on here but basically it saves having to rip the building apart to find the leak. Google leak detection specialist and you will see there are all quite a few companies specialising in it. They use specialist water leak detection equipment to non-intrusively find leaks. I don't fancy trying to dig out pipes in floors and walls to find a pre-existing leak on a 12 radiator system over 3 floors and a loftspace tbh. I know that the customer won't stand for that either.

 

[cr0ft]

Hi all, update on this. Added the leak sealer on 21/02/11. All seemed to be working ok (according to the homeowner) until the pressure started dropping off again over the weekend. I'm going back today to check the PRV, system pressure when fully charged and warm (i.e. the expansion vessel is functioning correctly) and also both the AAVs in the loft. I'm going to wrap some cling film around them and tape it to the pipe. When I pop back tomorrow if there's any expansion of the cling film I know air is escaping. This said, for the pressure drops we're seeing I would expect a huge amount of air to be escaping and there doesn't seem to be any air in the radiators at all.

I am aware that in a sealed system a pressure drop equates to a very small amount of water leaking out so unless anyone else has a good idea I think I've exhausted all the checks on the new install which just leaves checking the old pipework - a long and slow process!! I've looked for companies nearby with acoustic leak detection equipment but can't find any in Hampshire

 

[SimonG]

Tape a 1/2 litre coke bottle over end of prv pipework, it will collect any water if its passing slightly.

 

[cr0ft]

Yup, did pretty much the same thing with a plastic bag today and some duct tape. The householder is going to look tomorrow.

I'm pretty sure it's a small leak that's opening up on the legacy pipes from the vented system. Wasn't picked up during my pressure test so it must be happening when the system is heating up.

The house is spread over 3 floors with 2 mezzanine floors as well so it's going to be a case of getting hold of an infra-red camera to trace the leak I think! Always fun to play with new gadgets and easier than ripping out floors/walls aimlessly.

 

[wheeto]

Have you considered pressure-testing the pipework again? It might be that some sludge has been removed by the clean you'll have done during the changeover. This would confim your diagnosis before bringing expensive (?) 3rd party leak finders in.

 

[ratrace]

What happened with this mate?

 

[stevetheplumber]

id take the aavs of and replace with manuals just to take them out of the equation tape a plastic bag onto the prv pipework