Air in open vented system

[rkanaga]

We have an open vented system with a new Vaillent Eco tech boiler fitted 2 years ago, 2 Honeywell motorised valves and a Grunfos alpha 2 pump.

We had a leak from a rad pipe burried in screed in the living room. Very messy! Had to dig out a replace a section of pipe and them refill the system

It may have been leaking for a month or two before the damp became apparent

We also had the pump replaced 2 weeks before the leak was detected as it had become noisy

All was well for 6 weeks but now we are getting air and airlocks in the system, banging in the boiler, the boiler shutting off as the pump is not clearing the heat etc. when the pump (boiler and pump downstairs) starts and stops you can hear air gurgling around

I had been getting some air from one upstairs rad and the bleed valve by the hw cylinder over the past few months (before obvoiusly due to the leak with hindsight and after I presumed some resudual trapped air plus the aerated air after refilling?) but now curiously am not getting any despite there clearly being air in the system

the rads and hit water are getting hot but clearly the system is not running correctly with all this air in it

The f&e tank is filled and the ball valve is working. I'm going to tie the ball cock up to check for leaks tomorrow but there weren't any when I checked after the repairs


British Gas came and flushed round the air ( by using the service mode and turning the pump on and off etc) but 24 hours later we were back to square one!

Reslly at our wits end!

any suggestions would be very welcome

Thanks

Robin

 

[Killy Bing]

Imho sounds like the feed and vent has been poorly plumbed in, pulling air in from the vent

 

[rkanaga]

But the boiler was put in 2 years ago and only has been causing problems over the past 6 weeks?

 

[SimonG]

But the boiler was put in 2 years ago and only has been causing problems over the past 6 weeks?

Could have been causing problems since installation, but only become apparent with the current issue. Get yourself upto the F & E tank when system is running to see if it's pumping over. Check it on heating only, water only and on both at the same time.

 

[rkanaga]

Will do

thanks

 

[Egidio]

Vaillant ecotec would be a system boiler usually installed in a sealed sytem, it has a pressure vessel inside and requires a minimum pressure in order to work.
I am not sure why someone would leave the F & E tank in when you would only need a water mains supply and a filling loop.
Anyway, in order to take the air properly you need to have the system cold and manually open the motorized valves, also on top of the pump there is a auto air vent which should be open to take the air in pump.

 

[rkanaga]

Vaillant ecotec would be a system boiler usually installed in a sealed sytem, it has a pressure vessel inside and requires a minimum pressure in order to work.
I am not sure why someone would leave the F & E tank in when you would only need a water mains supply and a filling loop.
Anyway, in order to take the air properly you need to have the system cold and manually open the motorized valves, also on top of the pump there is a auto air vent which should be open to take the air in pump.

No it's definitely open vented

I think the ecotec can be used like this?

 

[Nostrum]

400 series is open vented

 

[rkanaga]

Could have been causing problems since installation, but only become apparent with the current issue. Get yourself upto the F & E tank when system is running to see if it's pumping over. Check it on heating only, water only and on both at the same time.

Checked and it is not over pumping into th f&e tatank tied the ball up to check for leaks, ill look again lalater thanks for all the help so far

 

[SimonG]

Check to see if the cold feed from the f & e tank is getting hot.

 

[rkanaga]

Check to see if the cold feed from the f & e tank is getting hot.

No the feed and expansion pipes are not hot and definitely not overpumping


thanks

 

[happyflyer]

No the feed and expansion pipes are not hot and definitely not overpumping


thanks

Now we are scratching our heads

 

[zzzjim]

Where work was done things may have been disturbed ,causing a slight leak ,not letting much water out ,but allows air in each time pump starts and water resisting getting up to speed . ( Inlet side of Pump/Plumbing )

( How gunky were things ? - many possibilities )

 

[happyflyer]

Do a proper timeline or we will be guessing for the next 50 posts

 

[rkanaga]

Do a proper timeline or we will be guessing for the next 50 posts

ok here goes


Oct 2011
20 year old open vent boiler with thermosyphon hot water replaced by fully pumped Vaillant ecotec 400 series, two Honeywell motorised valves. System flushed through and commissioned. Thermostatic valves fitted to upstairs rads. F&E tank in loft, boiler, pump and valves on ground floor, hot water cylinder on 2nd floor with bleed valve next to cylinder. Pipes on ground floor buried in screed, the rest beneath floorboards. New Grunfos pump fitted.

worked fine

Feb 2012 4 rads on 1st and 2nd floor removed for redecorating and refitted

March 2013 noticed air in upstairs rad (the one right above the old boiler position so probably 1st in system), pump also becoming noisy. Tied up ball cock and the F&E tank emptied overnight. Called BG who replaced pump with Grundfos alpha2 and said they couldn't see any obvious leak but to keep an eye on it(!)

April 2013 niticed damp in living room. Laminate taken up and leak located with thermal camera. Dug into screen to locate pipe Pipe to living room rad had split where it had been bent to go under gas pipe during original installation 30 years ago! system drained down and pipe cut out and replaced. The rest of the buried pipe work was ok and importantly had been wrapped in Denso tape when originally installed (thank goodness.)

All well for 6 weeks, but still getting air in upstairs rad.

2 weeks ago noticed pump noise again and then the next day there were airlocks in the system. Called BG again who flushed through the air. Extended the vent pipe as they said it was only 150mm not 450mm above the water level.

Next day the new pump was noisy again and there was again air in the system, banging, the boiler cycling on and off etc.

Called BG again who said that the pump that had been fitted 6 weeks ago was failing probably due to running dry before the leak was fixed. Replaced pump again and all was well.
Next day back to square one!



I cannot find any more leaks.
I have tied the ball cock up and so far the level is rock steady (6 hours)
The vent pipe does not empty any water when you start the system up
When the system was refilled after the leak repair corrosion inhibitor was put in the system
There is some verdegris around a couple of rad joints but no obvious leaks (probably been like that for years)

All this has only happened since the water leak and draining down the system to repair (although if was ok for 6 weeks after the repair before becoming airlocked.)

We ran the system only on the hot water circuit and it still became air locked so if it is drawing in air it must be somewhere in the limited boiler-pump-cylinder-FE tank loop?


I am baffled as to how the air is getting in!

Many thanks

Robin

 

[happyflyer]

Try this for a short while,

Manually open both Honeywell valves and lock them there
Turn our boiler stat down so at reduce the HWS does get too hot and burn someone
Open all your rads if the house get too warm control the temp with the boiler stat
let the programmer run 24 x 7 don't let the pump stop running

I am trying to establish if the valves are having an influence on the hydraulic before you chase your tail.

I know you say the vent in not pumping in over but are you really sure a small plastic container on a string just below
the vent will save you siting up there, it may only happen when the valves move, if you do test the vent with a container
ignore what I say above try the container first.

BTW who the hell does plumbing like that, pipe in a screed gas and heating, no no no no no, not ever

It like you say its too much of a coincidence that is started after the leak was fixed.

Where do you live.

 

[rkanaga]

Guildford

 

[happyflyer]

Guildford

I knew it wasn't up North, seriously we would never ever put copper in a floor screen like that and Gas steel ??? BTW Denso tape won't save you in a screed, how big of a job would it be to re-pipe out of the screed.

 

[rkanaga]

A big job but if there is no leak why would you want to do that?

 

[happyflyer]

A big job but if there is no leak why would you want to do that?

You will only know that there are no leaks when you have properly pressure tested the underfloor pipe, that simple test you did with the tank level proves nothing, you would need to apply some more static pressure over and above what is applied with the tank head, I would not trust any copper pipe in a screed and the solder fitting even less. To test the pipe you need to isolated it from the above circuit put a large pressure gauge 6" in diameter and pump it up, if you have had one leak under in the screed is it not possible there are others, whats the odds against it.

http://www.ukcopperboard.co.uk/literature/pdfs/Installation-Tips/Pressure-testing-piping-systems.pdf

 

[rkanaga]

Further Update. I tied a plastic bottle to the vent pipe and it was still empty 24 hours later, so no over pumping

Likewise the F&E tank level has not dropped over 24 hours so I presume no leak (bearing in mind happyflyer's comments above but when we DID have a leak the level dropped noticeably even without pressure testing the system.)

The how water is sort of working, but you can still hear air in the system and if you set the pump to anything less than III the boiler overshoots its desired temp and cycles off and on again repeatedly

 

[dancinplumba]

Ignore HF. There is air being drawn in somewhere, this will be on negative side of pump, poss on compression joints. Put pics up of pump area. Or there is corrosion of rads going on. As you have installed new rads this could be happening ?

 

[PeteWalker]

It's (just) possible that it's sucking air down the vent. Very unlikely but you see it occasionally when it "can't happen", due to strange scale build ups in the pipes. You can suspend a container with some water in it under the vent pipe to see if it gets sucked up - mark the level.

More likely if the level of the water in the f&e isn't far above the junction between the vent pipe and the main circulation. Sometimes you get mad-as-frog configurations.

Agreed, inlet side of pump is always a supect, again depending on configuration.

-

Blockages increase over time. Does the boiler seem like it's getting near boiling? Listen for "singing", feel pipes. Scale>> blockages>> overheating locally, makes things worse.

 

[dancinplumba]

It's (just) possible that it's sucking air down the vent. Very unlikely but you see it occasionally when it "can't happen", due to strange scale build ups in the pipes. You can suspend a container with some water in it under the vent pipe to see if it gets sucked up - mark the level.

More likely if the level of the water in the f&e isn't far above the junction between the vent pipe and the main circulation. Sometimes you get mad-as-frog configurations.

Blockages increase over time. Does the boiler seem like it's getting near boiling? Listen for "singing", feel pipes. Scale>> blockages>> overheating locally, makes things worse.

Read post 21

 

[PeteWalker]

Read post 21

I read it! This is different, it can SUCK AIR down the vent pipe, rather than the target of the test in 21, which was to look for water coming out.