Air Problem in Open Vented System after Boiler Change

[ThePook]

What makes you think your pipework (which has survived for decades) won't be able to take the relatively small increase in pressure from a sealed system?

I take your point. Honestly, its probably just a somewhat irrational fear of undiscovered leaks under floors. Genuinely, I believe it originates from discovering dry rot under the floor of our first house on day 3 of ownership, having skrimped and saved for years for a deposit, and being pennyless to sort it out quickly!

Oh and you have a manual vent on the return, I'd probably replace that with a bottle vent which would at least prevent any trapped air from being recirculated.

Good shout and an easy job for a quick win. Leave open all the time or close after initial fill and bleed? Worth putting one on the top flow into the DHW coil, too? Both places are manual at present.

But it doesn't alter the fact that the air shouldn't be there anyway.

My thoughts entirely, and why I want to remedy at source the air problem.

Mmm! I'd expect it to drop if water is being drawn into the h/ex.

What if the HEx was also somehow letting the air in? Long shot, I guess.

BTW what's a Monument gauge?

Sorry, Monument-branded water pressure gauge - on a hose with a 1/2 bsp female connector. Bought when our first house kept popping joints, and eventually proved that our incoming water mains was over 10bar at times - see above, sad times!

Thanks all for the constructive comments - appreciate you taking the time.

 

[gmartine]

A bottle vent does so automatically, yes I'd replace both manual vents. Intergas condenses all the time due to nature of hex, doesn't explain colour but may explain volume.

 

[fixitflav]

Thanks all for the constructive comments - appreciate you taking the time.

Keep us posted on F/E tank level and condensate production. I still think it's most likely the h/ex.

 

[ThePook]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Going to struggle to catch and check the condensate, also cook with gas, so volumes will be misleading. Will have a think on that one...

 

[fixitflav]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Going to struggle to catch and check the condensate, also cook with gas, so volumes will be misleading. Will have a think on that one...

As you do not appear to be losing water (out of the h/ex) checking condensate vs gas consumption won't tell you much.
The h/ex could still be drawing air in but not leaking water. I can't think of anything else, and you've tried nearly everything. I can see the installer will be loth to change the h/ex (or the complete boiler). Maybe if it's at your cost if it doesn't cure the problem.

 

[Last Plumber]

Also forgot, the condensate trap on the boiler seems to run quite often and has a black/dark dusty sediment in it. Is that normal?

It's normal to have a small settling of dark residue in the bottom of the trap if that's what you mean? It should be cleaned out at service time.

How is the Flow to the Cylinder Coil vented? (curious).

 

[Last Plumber]

Could a faulty hex explain foamy water in the primary circuit?

Too much inhibitor could do in my experience. It can be overdosed and end up like soap as it leaves the pump. Only seen it on very few occasions but it can.

 

[fixitflav]

Let the system cool tonight, much to the disgust of Mrs Pook, and the cold level in the tank is exactly the same as 24 hours earlier.

Just one thing, probably irrelevant to your problem but I'm curious. You said earlier the Evohome controls the hot water, and I can see in the pic the actuator has been removed from the HW valve. How does that work? What stops the HW getting too hot when CH is on?

 

[ThePook]

It's normal to have a small settling of dark residue in the bottom of the trap if that's what you mean? It should be cleaned out at service time.

How is the Flow to the Cylinder Coil vented? (curious).

Yes, that's what I mean about the trap - thanks for confirming.

The DHW primary coil had a manual vent on the top (flow) connection until this evening. I have fitted an AAV there tonight and on the top of the return to the boiler. Let's see, but not optimistic!

Too much inhibitor could do in my experience. It can be overdosed and end up like soap as it leaves the pump. Only seen it on very few occasions but it can.

Interesting, I have 1l of X100 in a 10 radiator system. Tested it with Sentinel's Quick Test kit, and looks spot on.

Just one thing, probably irrelevant to your problem but I'm curious. You said earlier the Evohome controls the hot water, and I can see in the pic the actuator has been removed from the HW valve. How does that work? What stops the HW getting too hot when CH is on?

The missing actuator is the CH flow, so the valve is full open. The HR92 radiator valve controllers open/close to control flow to each individual rad. If you download the Evohome manual, it is their preferred 'figure 4' installation. Works well, and means each room is a separate zone with time and temperature control. The right-hand BDR91 in the photo opens/closes the DHW zone actuator (mine is also hardwired via a conventional cylinder thermostat, so for safety it does not rely entirely on wireless control to limit water temperature). The total heat demand is calculated by Evohome and is controlled by the left-hand BDR91 wireless boiler relay in the photo.

 

[fixitflav]

The missing actuator is the CH flow, so the valve is full open.

OK, not for the 1st time, I jumped to the wrong conclusion!

 

[ThePook]

Ok, so tried a few more things:

The air can be purged out of all circuits if it is run with the boiler off. I can achieve silent flow whichever zones are open in this way.

If I fire the boiler, as soon as it reaches temperature (currently flow is set at 70C) I hear air bubbles coming out of the top of the boiler and through the pump.

If it is circulating through DHW or Auto Bypass Valve at the time, I get quite a large overshoot on the flow temperature (approx 8-10C) before the boiler modulates down. I am sure this is to be expected, as in either of these scenarios, the return temp is higher. But I guess it might explain why the noise is worse after either of these circuits have been active.

Thoughts?

 

[fixitflav]

Ok, so tried a few more things:

The air can be purged out of all circuits if it is run with the boiler off. I can achieve silent flow whichever zones are open in this way.

If I fire the boiler, as soon as it reaches temperature (currently flow is set at 70C) I hear air bubbles coming out of the top of the boiler and through the pump.

If it is circulating through DHW or Auto Bypass Valve at the time, I get quite a large overshoot on the flow temperature (approx 8-10C) before the boiler modulates down. I am sure this is to be expected, as in either of these scenarios, the return temp is higher. But I guess it might explain why the noise is worse after either of these circuits have been active.

Thoughts?

With those symptoms, it looks to me more and more like the h/ex. Maybe something expands when it's firing, causing a leak to open up. On the optimistic side, maybe there's a bolt or something loose, which can be easily fixed.
Presumably the boiler is recently installed so still under guarantee. Have you involved Intergas? I still think I would replace the h/ex, at their cost, naturally, if it cures it. It's not going to be that expensive, in the context of the problem, if it doesn't. You seem to have eliminated everything else.

 

[Dave M]

Sorry, don't understand that, is it something I said?

Cold feed from tank should be fitted in return ,on the photoits in wrong place. so cap off by air separator and connect to return at bottom of picture

 

[fixitflav]

Cold feed from tank should be fitted in return

That's how it was done 40-odd years ago, nowadays it's boiler - open vent - cold feed - pump. Cold feed preferably up and under, to avoid convection warming the F/E tank, hasn't got that here, but I doubt it's causing the current problem. Earlier arrangement caused seesawing between the vent pipe and the F/E tank, drawing aerated water into the circuit every time the pump starts and stops.

 

[ThePook]

Hi all,

Apologies for the long gap between posts, but I have let this run for a couple of weeks with the flow temperature at 65degC. The result - total silence.

On Friday night I turned it back up to 70degC. The bubbles are back with a vengeance!

The boiler manufacturer's customer service have not been helpful at all, which when you consider the cost of a boiler is very disappointing. Wondering if I might end up forking out of my own pocket for my GSR installer to fit a new heat exchanger, but considering the lack of interest from the manufacturer, I feel like I would rather put the money towards a different brand of boiler altogether.

Any other thoughts before I bite the bullet?

Thanks in advance all.

 

[Steve57]

I installed a Spirovent RV2 air eliminator on the inlet to the pump. No apparent improvement, even though it was definitely ejecting air!

Isn’t the Spirovent supposed to be fitted on the outlet of the boiler as near as possible to the boiler?

 

[ThePook]

Isn’t the Spirovent supposed to be fitted on the outlet of the boiler as near as possible to the boiler?

Yes, that's where it is - on the flow, between boiler and pump.

 

[John.g]

Did you finally get a fix for your problem?

 

[fixitflav]

I have let this run for a couple of weeks with the flow temperature at 65degC. The result - total silence.

I can understand you want to get to the bottom of it, but is there a problem leaving it like that? It should keep the house warm enough now the worst of the weather is (fingers crossed) behind us. It might even save some money - more condensation. If you do want to tackle it again at least you can do it in the summer.

 

[John.g]

A bit late in the day for any advice but better late than never, that UPS2 is a A rated pump with two modes of operation, fixed speed or proportional pressure (PP) control, and while it shouldn't give any problems on fixed speed 1 ( a 4M pump at this setting) it may be worth trying it (if not already done so) in one of the PP settings, say 2, if OK at 70C increase it to 3 and see what happens.

 

[Dave M]

Cold feed should be taken to the bottom part of return ,as it’s circulating on the least resistances.
Do that and should stop problem

 

[ThePook]

So, long time no post - sorry for that.

Have finally bitten the bullet and had the system sealed with an 18l expansion vessel, its holding 1.5bar cold nicely, and minimal increase when hot due to decent EV size.

However - absolutely no change whatsoever to the noise. I still hear bubbles travel out of the boiler, through the pump and into the radiators as the boiler reaches temperature.

Any more ideas?

Surely it has to be something to do with the boiler as it runs silently cold and only when it hits 70+ on the flow temp does the noise start?

How about if I piped-up a simple boiler->pump->1 radiator->boiler loop in the garage for test purposes? If it still made the noise, then could I safely assume its the boiler at fault? If so, then what, as the boiler manufacturer didn't seem to want to help when this first started.

Thanks in advance all.

 

[Danb]

Not read through all the post so might be off the mark abit, but you havent just got a blocked or partially blocked cold feed. As system heats boils water seperateing the o2 from the h20 causing air, just a thought.

 

[Dave M]

Hi All,

First post here, so please be kind!

I am currently having a lot of trouble with air and related noise in my open vented heating system. Long story, with lots of things tried already, so please bear with me…

Firstly, a photo of the heart of the system in the garage as it is today (lots of spare cable length to allow me to move bits!):https://i.*********/FPl6NRA.jpg

The system originates from 1970, fully pumped, 9 radiators, 1 towel rail and a vented indirect DHW cylinder. Two-storey house, gas boiler, pump, zone valves in the garage, header tank in the loft. I changed all the radiators about 3 years ago and installed a Honeywell Evohome system with TRVs on every rad plus hot water control kit and an automatic bypass valve I added when I added the TRVs. The system was Y-plan at this time. Worked fine, no air problems ever, drained and filled fine for the radiator replacements, but the 35 year-old boiler always kettled badly. Always dosed with inhibitor. All plumbed in soldered copper, suspended floors throughout, so pipes not buried in screed.

Recently, the boiler was changed – system flushed, new Intergas HRE OV condensing boiler, Magneclean Pro2 on return, new Grundfos UPS2 15-50/60 pump on flow, taller towel rail, new header tank in loft (only ’cos the old one didn’t have a lid!), converted to s-plan (but heating zone valve locked open as Evohome does the zoning – recommended ‘figure 4’ solution from Honeywell). The other thing that was changed at this time was that the 'Registered Professional Gas Engineer' installer converted to ‘combined feed and vent’ (single 22mm to bottom of header tank, tee’d in just before the pump on the boiler primary flow, flow/return done correctly at boiler). System is dosed with Sentinel X100 and tested to be the correct strength. The filter is always very clean.

The header tank is (and always was) approximately 4.5m above the pump, and 1.7m above the top of the new towel rail, which is the highest part of the system.

Ever since this, I have not been able to get all air out of the system (or is it getting in?). The radiators make a terrible noise (sounds like ball bearings or gravel being fired through the TRV’s) which I am sure is air or gas bubbles. This is worst first thing in the morning, or when only 1 or 2 radiators are calling for heat. I have bled it literally tens of times bottom-up (all rads, pump, DHW cylinder, filter), the gas doesn’t burn or smell, so I am confident not a chemical/corrosion problem. Level in header tank is fine (always above outlet, always below overflow).

Things that have been tried (in chronological order):

1. Pump has been tried on all 3 speeds (it actually circulates fine even down at 1). No improvement.

2. I noted that the primary flow actually went slightly downhill before joining the vent pipe to the loft, so the installers (who are very helpful) returned, installed a Tower air separator (type without separate cold feed) and re-routed the pipe to run uphill. No improvement.

3. I installed a Spirovent RV2 air eliminator on the inlet to the pump. No apparent improvement, even though it was definitely ejecting air!
4. I isolated the flow at the pump valves and return at the filter, then connected a hose pipe to the drain point at the bottom of the boiler. I watched in the tank in the loft while somebody else turned the hose on – there was a huge belch of air into the header tank, suggesting that it was trapping in the feed/vent at some point. No improvement.

5. Based on point 4 above, I traced the feed/vent and found that there were significant unavoidable horizontal runs (crossing floor joists) and dips in it, so possible air locks/traps. I therefore moved the header tank in the loft, and made a new route for a new 22mm feed/vent, with significant uphill slope all the way to the loft. Guess what? No improvement.

6. I ran a separate 15mm cold feed from the loft, converted the 22mm to a vent over the tank (bend 450mm above water level), tee’d in just after the Tower separator in the boiler flow, before pump inlet (to replicate the layout of the version with the cold feed). In other words, back to a properly piped separate cold feed/vent. I.e. Boiler Flow->Tower Separator (with Vent Pipe)->Cold feed->Pump. Both pipes have nice constant fall from loft to boiler, system fills easily, no pumping over. No improvement.

7. I changed the pump valves, in case of air leak around the spindle on inlet side. No improvement.

So this is where I am today, with no improvement! As I understand, the neutral point is at the cold feed connection (approx. 0.42bar or 4.2m water), so the only section that could be under negative pressure and could conceivably admit air at any point is the short run of pipe (all soldered connections) down to the pump inlet. Is that correct?

The installers want to convert to a pressurised system, but I am very reluctant due to the nearly 50 year old pipes under floors and I sense that it would mask the problem, not cure it. I would really like to understand the problem.

Is there anything wrong with the current vent/feed/pump layout?
Could the pump itself be sucking in air?

The only very minor point in the piping design I know about is that all heating returns tee into the return line after the DHW return, but I don’t think this relates to my air troubles at all, and I get no reverse circulation in the summer.

Sorry for the very long post, but I wanted to put as many details of the steps taken to date as possible.

I would be extremely grateful for any thoughts you have.

The Pook

Hi All,

First post here, so please be kind!

I am currently having a lot of trouble with air and related noise in my open vented heating system. Long story, with lots of things tried already, so please bear with me…

Firstly, a photo of the heart of the system in the garage as it is today (lots of spare cable length to allow me to move bits!):https://i.*********/FPl6NRA.jpg

The system originates from 1970, fully pumped, 9 radiators, 1 towel rail and a vented indirect DHW cylinder. Two-storey house, gas boiler, pump, zone valves in the garage, header tank in the loft. I changed all the radiators about 3 years ago and installed a Honeywell Evohome system with TRVs on every rad plus hot water control kit and an automatic bypass valve I added when I added the TRVs. The system was Y-plan at this time. Worked fine, no air problems ever, drained and filled fine for the radiator replacements, but the 35 year-old boiler always kettled badly. Always dosed with inhibitor. All plumbed in soldered copper, suspended floors throughout, so pipes not buried in screed.

Recently, the boiler was changed – system flushed, new Intergas HRE OV condensing boiler, Magneclean Pro2 on return, new Grundfos UPS2 15-50/60 pump on flow, taller towel rail, new header tank in loft (only ’cos the old one didn’t have a lid!), converted to s-plan (but heating zone valve locked open as Evohome does the zoning – recommended ‘figure 4’ solution from Honeywell). The other thing that was changed at this time was that the 'Registered Professional Gas Engineer' installer converted to ‘combined feed and vent’ (single 22mm to bottom of header tank, tee’d in just before the pump on the boiler primary flow, flow/return done correctly at boiler). System is dosed with Sentinel X100 and tested to be the correct strength. The filter is always very clean.

The header tank is (and always was) approximately 4.5m above the pump, and 1.7m above the top of the new towel rail, which is the highest part of the system.

Ever since this, I have not been able to get all air out of the system (or is it getting in?). The radiators make a terrible noise (sounds like ball bearings or gravel being fired through the TRV’s) which I am sure is air or gas bubbles. This is worst first thing in the morning, or when only 1 or 2 radiators are calling for heat. I have bled it literally tens of times bottom-up (all rads, pump, DHW cylinder, filter), the gas doesn’t burn or smell, so I am confident not a chemical/corrosion problem. Level in header tank is fine (always above outlet, always below overflow).

Things that have been tried (in chronological order):

1. Pump has been tried on all 3 speeds (it actually circulates fine even down at 1). No improvement.

2. I noted that the primary flow actually went slightly downhill before joining the vent pipe to the loft, so the installers (who are very helpful) returned, installed a Tower air separator (type without separate cold feed) and re-routed the pipe to run uphill. No improvement.

3. I installed a Spirovent RV2 air eliminator on the inlet to the pump. No apparent improvement, even though it was definitely ejecting air!
4. I isolated the flow at the pump valves and return at the filter, then connected a hose pipe to the drain point at the bottom of the boiler. I watched in the tank in the loft while somebody else turned the hose on – there was a huge belch of air into the header tank, suggesting that it was trapping in the feed/vent at some point. No improvement.

5. Based on point 4 above, I traced the feed/vent and found that there were significant unavoidable horizontal runs (crossing floor joists) and dips in it, so possible air locks/traps. I therefore moved the header tank in the loft, and made a new route for a new 22mm feed/vent, with significant uphill slope all the way to the loft. Guess what? No improvement.

6. I ran a separate 15mm cold feed from the loft, converted the 22mm to a vent over the tank (bend 450mm above water level), tee’d in just after the Tower separator in the boiler flow, before pump inlet (to replicate the layout of the version with the cold feed). In other words, back to a properly piped separate cold feed/vent. I.e. Boiler Flow->Tower Separator (with Vent Pipe)->Cold feed->Pump. Both pipes have nice constant fall from loft to boiler, system fills easily, no pumping over. No improvement.

7. I changed the pump valves, in case of air leak around the spindle on inlet side. No improvement.

So this is where I am today, with no improvement! As I understand, the neutral point is at the cold feed connection (approx. 0.42bar or 4.2m water), so the only section that could be under negative pressure and could conceivably admit air at any point is the short run of pipe (all soldered connections) down to the pump inlet. Is that correct?

The installers want to convert to a pressurised system, but I am very reluctant due to the nearly 50 year old pipes under floors and I sense that it would mask the problem, not cure it. I would really like to understand the problem.

Is there anything wrong with the current vent/feed/pump layout?
Could the pump itself be sucking in air?

The only very minor point in the piping design I know about is that all heating returns tee into the return line after the DHW return, but I don’t think this relates to my air troubles at all, and I get no reverse circulation in the summer.

Sorry for the very long post, but I wanted to put as many details of the steps taken to date as possible.

I would be extremely grateful for any thoughts you have.

The Pook

The cold feed going to the aerater is in the wrong position .cap it off and move it down to the return pipe at the bottom.pumps pulling water down from that feed because of the least resistance. Ok

 

[John.g]

So, long time no post - sorry for that.

Have finally bitten the bullet and had the system sealed with an 18l expansion vessel, its holding 1.5bar cold nicely, and minimal increase when hot due to decent EV size.

However - absolutely no change whatsoever to the noise. I still hear bubbles travel out of the boiler, through the pump and into the radiators as the boiler reaches temperature.

Any more ideas?

Surely it has to be something to do with the boiler as it runs silently cold and only when it hits 70+ on the flow temp does the noise start?

How about if I piped-up a simple boiler->pump->1 radiator->boiler loop in the garage for test purposes? If it still made the noise, then could I safely assume its the boiler at fault? If so, then what, as the boiler manufacturer didn't seem to want to help when this first started.

Thanks in advance all.

I assume the expansion vessel is connected just before the pump inlet, if so, then the pump suction must run at 1.5 bar and the pump discharge at the pump head+1.5 bar, say 1.8 bar so very unlikely that pump cavitation is a problem.
If you are still getting air in the system then you should see the expansion vessel pressure rising a little, if the air displaces say 1 litre of water then you might see a increase of 0.2 to 0.3 bar even with that 18L expansion vessel.
Its hard to conclude that the boiler isn't the problem, you have checked that the pump is orientated correctly, can't remember if you tried it on any of the PP settings at 70C +.

You could fit a manual by pass between the flow and return close to the boiler, get the boiler up to say 80C, shut the power off to the boiler, open the manual by pass fully and then shut the boiler flow and return valves and restart the pump, you will then be circulating water without the boiler in the loop and see if the problem still persists, you may have to vent air first before doing this test. I assume that you can isolate the boiler flow&return external of the boiler casing as you cannot remove this.

 

[Josephalex]

Hi, Put a bungee strap around the ball valve and clip it up so no water can enter the tank, and monitor the water level. Thanks.

 

[John.g]

This thread is over 3 years old but it would be great to know if ThePook ever solved his problem as it only occured when the flow temperature was > 70C, he converted the system to a sealed system with no change.