Air in Open Vented HW system

[nez_pottage]

Hello all. Just looking for some advice on an Open Vented system in a house we moved into before Christmas. We've had a few dodgy parts changed on the system by a plumber, but he's now out of the country travelling for a few months, and I wanted to some extra advice / pointers.
Initially one small radiator wasn't performing as well but the bearings on the pump were on the way out, as was the 3 way valve, so they have been replaced, system left for 2 weeks with X800 and cleared out again (every system drain looked clean) and filled with x100.
That rad is now better, but the out pipe doesn't get as hot, and the rad isn't baking like the others. However, I can't find the manifolds and popping up the carpets isn't an option at the moment.
Since we've had the work done though (and possibly before as we haven't been in long) there seems to be a lot of air in the system, especially in the HW circuit rather than the CH.
All rads have been bled ok.
What we are finding is that when the HW is on, there is a lot of air noise in the main flow / return pipe. I can't seem to bleed the air out as there is no nipple valve on that circuit.
But what I have noticed is that the system expands a lot, and tends to push through the cold feed (thinner pipe) instead of using the expansion pipe (thicker).
See the diagram to show how they all link together.
Also what I have noticed, which is maybe how the air is pulling in, is whenever the HW turns off, there is a jet of water pushed into the F&E tank.
I know this because if I close the feed, water pushes out of the expansion when you turn off the HW. Usually you just see the movement in the tank from where it's coming back up the feed pipe.

On the whole, the system works fine. No knocking, more air flow noises, and drip noises in the boiler and the odd rad.

I've tried lowering the water level in the F&E and bending the ball arm, but tbh could only drop it by maybe 2 inches but it is less than half full now.

The other thing to note is that the boiler only stays on for around 2 minutes then shuts off for maybe 4 and goes back to the same. It doesn't seem to stop teh rads or water getting hot, but in case it relates to anything?

Any other tips, as I can't really get a plumber in right now I guess.

 

[John.g]

Can you post the pump make, exact model and present setting. ( I see thats its a Grundfos UPS3) so pump settings please.

 

[nez_pottage]

Thanks John. The pump is a Grundfos UPS3 15-10/65 130
I've tried different settings between constant 1/2/3 although the plumber left it on 3. The manual suggest 3 will help auto vent, but it doesn't seem to make a difference.
Constant curve didn't seem to match my system, and i'm not sure if proportional pressure is right or not, so haven't used. Just stuck to old school constant pumping.
With this pump there doesn't seem to be a bleed screw and it reads like it self vents.
I've looked high and low for some sort of manual vent on the HW system but I can't see one.

 

[John.g]

Ok, First things first, you say the system was drained a number of times so that will rule out any blockage where the cold feed tees into the vent ( a favourite blockage point), I see there is a isolating valve on the cold feed, just make sure that this is fully open, if it's a gate valve, close it and then fully open it, it should take 4 or 5 full turns.
I know grundfos suggest fixed speed 3 for venting but this is way too high on a vented system.
Even fixed speed (constant curve) 1, which I presume you have it on now is fairly high at 4.2M but really shouldn't cause pump over or pump back through the cold feed. You have two CP settings, CP1 is 3M & CP2 is 4.5M, and, two PP settings, PP1 is 2.0M & PP2 is 3.7M. IMO CP2 is too high and PP1 is too low. Suggest c/o to PP2 (3.7M) and see how that performs, if OK and rads are satisfied etc with no pump over/pump back then leave it there as that head will fall if any rads are closed in with TRVs or whatever. You could also try CP1 (3M, constant) and check again, as above. Before doing anything apart from checking that cold feed isolating valve, with boiler/circ pump off vent all the rads again and continue to do so after c/o to PP2.

 

[nez_pottage]

Thanks for the tip John. The flow is certainly a lot quieter on PP2, and rads seem to warm up ok, but after a few days there is still the bubbling / swashing sound in the pipes when the HW is on. Not so much on the CH.

I was also having a bit of time in the loft with the expansion pipe. If I turn off the cold feed, and cover the expansion with my thumb, you can feel the system almost sucking air in. But with the cold feed open, there is very little vacuum there, but you can see movement of the water in the tank. Makes me wonder if the system is sucking air in at the same time as water from the tank maybe, and i'm wondering why.

The only relating thing I have read is maybe for me to get a hose from the outside tap, and run it into the expansion into the cold feed. Open up the 3 way on manual, and force fill the system up. Is that something to consider, or have you got any other advice?

Thanks

 

[John.g]

Yes, you could consider that but your testing would indicate that both vent and cold feed are clear but it certainly can't do any harm as the slightest blockage in either can create a imbalance even though that would seem unlikely in your case as the schematic shows that the vent and cold feed are combined. If they are, as shown, very close to the pump flow then that may be acting as a eductor and creating that suction effect. I have a similar system but the cold feed is teed into the vent just adjacent to the F&E tank, you might consider cutting and capping the (blue) feed where it is presently teed into the vent and teeing into the vent straight from the isolation valve and that may cure the problem.
You say that the problem is worse on HW, that may be because there is a greater flow (higher velocity) through the system resulting in a greater suction effect on the feed/vent.
Your schematic shows both a bypass and a balancing valve on the HWC coil, I would note the setting of these, if the balancing valve (on coil return) is fully open, shut it then open it one full turn, run the system on HW only and see what effect it has, you can also check the position of that by pass but be careful as that may be required to give the boiler a minimum flow.
Its very difficult to offer a definitive cure as these vented systems can be a PITA especially after a pump changeout + system flush as it may be one or the other causing the problem, I assume your system was OK before??.

So, maybe do that hose flush first, then adjust the HWC coil valves next (or vica versa) and then do the piping mods, especially if you are handy yourself.

Edit: Just looking at your schematic again, I assume that the vent/cold feed are on the pump FLOW, is that correct??., if not back to the drawing board.
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Should have said from boiler flow and pump suction.

 

[nez_pottage]

Cheer John.
I think the HW valve has always been on full, and not sure about the bypass as different work has been done. As we moved in in December and had issues, we don't know the full history to be honest.
I will try turning the cylinder exit valve down tomorrow.
Piping mods are not for me, but someone else mentioned dropping that cold feed more direct rather than it teeing into the expansion vent first. (see pics, he suggested maybe a H setup rather what I have inherited)
Vent/cold feed, yes on the flow from the boiler to the pump.

See pics below

At the top of the first photo the bend in the middle right side is the cold feed and the verticle pipe on the left is the vent.
6 inch down from their T, is a T going right which is the flow meeting the feed/vent and kicking right to the pump
One note, whilst the pump looks upside down, it's just the controls mounted the other way around to suit cabling access. The pump is firing downwards toward the 3 way

 

[John.g]

Just throttle in the cylinder balancing valve, (shut it, and then open it 3/4 to 1 full turn open) check that by pass, carefully count the turns necessary to close it, if it is full open, I would close it and open it a max of a 1/2 a turn. See how this works out and post back.
Re pipe mods, you could bring the cold feed down to join the pump inlet but it must be kept not more that 150mm from the vent, personally I don't think that would achieve anything much as you already have the vent&cold feed combined.
Also stick a cork in the vent and watch and see what's happening with that cold feed when pump stops etc and post back.

 

[nez_pottage]

Cheers John,
Ran it now for a few days on reduced valves. Doesn't seem to make any difference to the sloshing sound, that I am now convinced is coming from inside the cylinder.
With a cork on the vent, i'm tempted to say the cold feed now gets hot most of the way up the pipe, and the vent only gets warm for the first few inches. When the pump stops there is a little water movement in the expansion tank, but not loads.

Right now it feels to me like that is air trapped in the cylinder that won't push out, even with the pump set to highest, but I could be wrong.

 

[John.g]

I would remove the cork (now) and go back to PP2 as max speed will IMO cause even more air ingress, air can be very difficult to get rid of in a cylinder coil especially if it's located some distance away horizontally from the vent pipe, generally, a auto or manual air vent located just before the cylinder coil entry will clear the air.
You could still try "the hose" and then refill the system very slowly which I do on the very rare times that I have drained my system down, vented system with combined cold feed & vent, combined right at the F&E tank.
Really can't suggest anything more meaningful at the moment.
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I should have said as well that having the circ pump on the 1st floor is probably not helping either, especially in a vented system, have seen it on unvented but not on vented systems. The vent pipe (top) should be ~ 450mm above the F&E tank water level.
Just for interest attached is my combined cold feed & vent.

 

[nez_pottage]

Tried the hose trick - turned off system, opened 3 way valve on manual, emptied F&E tank and tied ball cock up.
Hose into old feed, slow to start then a little faster.
Quite soon got a big splurt of air out of the vent followed by a nice trickle of water. Then turned hose up and had some more air, but fairly soon the tank level got too high so i stopped.

Ball cock back on, the top of the vent for the F&E sits at about 360mm. I tried bending the ball cock arm but I think i need to take it off completely to bend it enough to make the water level drop to 450mm below highest point.

Ran HW for a bit. Definitely less gurgling, but still some gurgling at the boiler. Gonna sit on it tonight, and maybe try again tomorrow.

So am i right in thinking I need to lower the F&E level ideally.
Also, would the hose trick work better if I corked the vent first to build up some pressure?

Pics of F&E if it helps at all?

 

[SJB060685]

So am i right in thinking I need to lower the F&E level ideally.

The level of water in feed and expansion tank is usually only a few inches when cold. If your vent is not extended a minimum of 450mm above cold fill line then as was said above this could cause unwanted venting over if there were any sudden pump surges. I would personally extend the vent but this requires a plumber and is not considered essential during these troubling times when the system is working and safe.

 

[John.g]

I wouldn't/couldn't recommend bunging the vent while using the hose, I think you have proved that there are no blockages.
Reducing the level in the F&E tank while it may give you the "450 mm" will result in a reduced head of cold water at the pump suction and will possibly increase the back flow through the cold feed but you can observe if this happens, ideally, the vent pipe should be extended.
Also, check the boiler flow temperature, you could reduce it to 65C if it's presently higher and see what effect this has.

 

[nez_pottage]

Cheers both.
Yep, definitely a plumber job once the world returns.
Right now it's all working, but the level of air bothers me with the noise, and the possible rusting in the pipes if left too long.
Short term, I'll have another crack at hosing more air out and aim to get that vent raised when I can. I would consider doing it myself, but I assume just adding two lots of 100mm pipe with compression joints isn't the right thing to do, and ideally the vent pipe should be a single piece?

Why would that vent be so low? Is 450mm quite a recent ish number, bearing in mind this is an early 80s house potentially with the original plumbing.
Thanks all.

 

[John.g]

The 450mm height has been there for decades.
Compression fittings are fine to use.
Have you checked the boiler flow temperature? and is the boiler gas or oil and output if available.
Also assume you are still on PP2 pump setting.

 

[nez_pottage]

Boiler flow temp I wasn't sure. It's a gas boiler - ideal classic HE15. Stat is set to 4/6.
But I found the manual which says 66C is 3/6 so I will reduce it now.
Yeah pump is down to PP2. I'll check that the stat on the cylinder is on 65 too.
Compression I'm happy with and have a pipe slicer, and some spare 15mm pipe too. Just need the fittings which I may be able to do on click & collect. So literally split the pipe, add 100mm to raise level, and add 100mm to teh add to bring it back to just lower than the tank sides?

 

[John.g]

The vent is 22mm or so?

 

[nez_pottage]

Good point. It is. Cold is 15 I think. Vent is a little wider.
One for a pro then maybe.

 

[SJB060685]

The vent should always be a minimum of 22mm and cold feed 15mm. This increases with KW output of boiler but don't worry about that, I'm talking large increases and yours is a small domestic appliance

 

[John.g]

Boiler flow temp I wasn't sure. It's a gas boiler - ideal classic HE15. Stat is set to 4/6.
But I found the manual which says 66C is 3/6 so I will reduce it now.
Yeah pump is down to PP2. I'll check that the stat on the cylinder is on 65 too.
Compression I'm happy with and have a pipe slicer, and some spare 15mm pipe too. Just need the fittings which I may be able to do on click & collect. So literally split the pipe, add 100mm to raise level, and add 100mm to teh add to bring it back to just lower than the tank sides?

Well, you could make a few relatively simple changes to the pipework with a few compression fittings, drain the F&E tank, cut the 15mm pipe, where marked, and fit a 15mm cap (on righthand end), cut the 22mm vent and install a 22mm to 15mm T, remove the piece of 15mm pipe from the F&E tank and install a new piece of 15mm from the isol valve to the T (may also require a 45 deg elbow), you will then have a system almost identical to mine,.(apart from the circ pump elevation which my be the main culprit). If it doesn't work out you can reverse it quite easily and the whole exercise would only cost a tenner or so.?

 

[Donametchi]

View attachment 43090Hello all. Just looking for some advice on an Open Vented system in a house we moved into before Christmas. We've had a few dodgy parts changed on the system by a plumber, but he's now out of the country travelling for a few months, and I wanted to some extra advice / pointers.
Initially one small radiator wasn't performing as well but the bearings on the pump were on the way out, as was the 3 way valve, so they have been replaced, system left for 2 weeks with X800 and cleared out again (every system drain looked clean) and filled with x100.
That rad is now better, but the out pipe doesn't get as hot, and the rad isn't baking like the others. However, I can't find the manifolds and popping up the carpets isn't an option at the moment.
Since we've had the work done though (and possibly before as we haven't been in long) there seems to be a lot of air in the system, especially in the HW circuit rather than the CH.
All rads have been bled ok.
What we are finding is that when the HW is on, there is a lot of air noise in the main flow / return pipe. I can't seem to bleed the air out as there is no nipple valve on that circuit.
But what I have noticed is that the system expands a lot, and tends to push through the cold feed (thinner pipe) instead of using the expansion pipe (thicker).
See the diagram to show how they all link together.
Also what I have noticed, which is maybe how the air is pulling in, is whenever the HW turns off, there is a jet of water pushed into the F&E tank.
I know this because if I close the feed, water pushes out of the expansion when you turn off the HW. Usually you just see the movement in the tank from where it's coming back up the feed pipe.

On the whole, the system works fine. No knocking, more air flow noises, and drip noises in the boiler and the odd rad.

I've tried lowering the water level in the F&E and bending the ball arm, but tbh could only drop it by maybe 2 inches but it is less than half full now.

The other thing to note is that the boiler only stays on for around 2 minutes then shuts off for maybe 4 and goes back to the same. It doesn't seem to stop teh rads or water getting hot, but in case it relates to anything?

Any other tips, as I can't really get a plumber in right now I guess.

Have you tried balancing the system.?I.e turning down the lock shield valves throughout the house