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

 

[dancinplumba]

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.

My bad

 

[rkanaga]

Ok bottle of water now suspended at the end of the vent

 

[dancinplumba]

Ppobs with this tho' is that the water will get sucked down pipe but will not indicate whether its getting sucked down far enough for air to be sucked into system

 

[dancinplumba]

Can you put pics up of pump area and where your feed and vent pipework connect to system ?

 

[Killy Bing]

Ok bottle of water now suspended at the end of the vent

the end has tqo be dipped into it

 

[rkanaga]

ok

I think my diagram is accurate as far as I can tell
thanks again

 

[nickelarsed]

looks like vent and feed wrong way round?

 

[rkanaga]

Really? Why?

surely the vent should be higher than the feed?

 

[nickelarsed]

the feed should always be between the vent and the pump - to stop it drawing air in, was what I was taught. But I'm not really a heating bloke so the others may have better ideas

 

[zzzjim]

Feed constricted a bit by ISO valve ( would a full bore one do better )

 

[nickelarsed]

what setting is the pump on?

 

[rkanaga]

3, constant speed

anything less and the boiler won't start up

 

[PeteWalker]

Ppobs with this tho' is that the water will get sucked down pipe but will not indicate whether its getting sucked down far enough for air to be sucked into system

Fair comment, but it would indicate something worth investigating if the water disappears.

Seeing the pictures, that's not going to happen though. There's no possibility of a difference in pressure between the feed and vent with them connected together like that! (So I can't see what BG man's line of thought was in increasing the vent loop height )

[Ignoring the chrome valve which shouldn't really be there, for now...]

If the pump's pumping some air, however it gets there, why isn't any getting stuck in the cylinder feed? Is there some sort of air-trapping upstand at the vent point (on the cylinder feed) or is it straight on say an elbow?

OK corrosion causes "air inthe system" symptoms, but not in a day or two.


Ummmm.......

 

[zzzjim]

duplicate

 

[PeteWalker]

I've just noticed the Automatic Air vent in the middle picture. Is that on the cylinder primaries?
If so, are you leaving its cap done up? If not, then air would escape and you wouldn't notice it. If you do it up, then it would be quite hard for air to escape at all from the system on HW only, because the path to the vent is long and horizontal (not ideal).
They often leak a bit so get left done up - :bulb2:that could be the entire recent problem, instigated by recent works.


Having a "combined feed and vent" is usually OK, though strictly speaking only if the manufacturer says so.
Exactly what boiler it? It'll be an Ecotec "plus 415" or similar.

Where you've written "PRV" by the way that's an ABV - Automatic Bypass Valve . Probably a DU145. Can you see what pressure it's set to?

 

[PeteWalker]

415 not 515.....

 

[rkanaga]

Ecotec plus 428

the valve is set on 2

thanks

 

[zzzjim]

Beginning to look like a system best not drained down , a special filling technique may be required , as it looks like air trapped in horizontal part of combined feed will be fed back into system.

Once all air is out it may well behave better ( Slower pump speed ? )

Since there will be no springyness in system to cause demand from feed as things get moving !

Would

a) Making sure horizontal run is absolutely true
​

b) Giving horizontal run to vent pipe a slight rise toward vent
Improve things ?

(or if it cannot deal with Air, how safe with steam)
​

 

[PeteWalker]

Yeah it would be a bit hesitant to fill. Seen worse though.

b) , pipe rising toward the vent, would surely be a good thing
Steam would "blow" out so I don't think that's a worry.
As mentioned the chrome valve shouldn't be there in case it became closed/clagged up, which could prevent a water supply to the system.

How's that Auto Air Vent?
If there IS a continuous collection of "air" then a chronic problem is indicated, such as a micro leak(air going in) or corrosion.
I'm hoping that a short term air collection, connected with it being shut, could be the acute one.

 

[rkanaga]

Yeah it would be a bit hesitant to fill. Seen worse though.

b) , pipe rising toward the vent, would surely be a good thing
Steam would "blow" out so I don't think that's a worry.
As mentioned the chrome valve shouldn't be there in case it became closed/clagged up, which could prevent a water supply to the system.

How's that Auto Air Vent?
If there IS a continuous collection of "air" then a chronic problem is indicated, such as a micro leak(air going in) or corrosion.
I'm hoping that a short term air collection, connected with it being shut, could be the acute one.

OK the thread has gone a bit quiet now. Thank you for all your contributions. I thought I would update things.
I've done the bottle test, suspending a plastic bottle beneath the vent pipe, both empty and filled to a mark (with the end of the vent pipe in the water of course!) I've also tied up the float valve for 48 hours.


There is no drop in the FE tank level so no obvious loss of water
The vent pipe is not pumping over or sucking back up

The banging and loud whooshing in the boiler and pump has stopped.

I have found that if you run the Grundfos alpha2 on constant speed 2, then it is quiet, runs at around 15watts and the boiler does not cycle on and off. With the water temp set to 70 on ththe boiler and 60 on the cylinder stat the actual temp goes up to 50 and then very slowly edges up to 60, but without cycling. The water cylinder heats up ok, but I'm not sure how it would cope with water and heating at this speed?

If you set the pump to constant speed 3 (as we were told to by the BG man)then the boiler rapidly heats the water to 70 but then cycles off. It seems unable to maintain a steady state. Odd as I would have thought it would be able to maintain higher temps better at this higher flow rate? The pump runs at 40w but is noisy. It was quiet at this speed only for 24 hours after it was put in then the rumble returned.

There are small amounts of air now appearing in the auto bleed valve by the cylinder.

BG are coming tomorrow to see what they think. I wonder whether actually the problem is not that the pump was changed but that it was changed to the newer type of pump (plus some trapped air from. When the system was drained?) Maybe constant speed 3 is simply too fast and is cavitating? Is speed 3 on an alpha faster than 3 on the old style Grundfos? I have tried the auto setting and the PP2 (proportional pressure) but they seem not to be able to pump fast enough to make the boiler start. Maybe I haven't waited long enough for the pump to 'learn' when in these modes though?


If the solution is to leave it in speed 2 then that would be ok, I just want to make sure I am not leaving a potential problem (eg corrosion) which is going to rear its head a few months down the line.

Thanks again


Robin.