Hello, I have a relatively new Nike F2050-10 + SMO 40 system (installed a couple of weeks ago). The installer also fitted a Level 3 bundle for me (the one with the Axioma heat meter and 2 MID electricity meters because I have a separate circulation pump in the plant room).
I’ve got a bit of heating and hot water running to stir up the crud in the system with the installer due to come back to run a power flush (the system is currently dosed with Addy MC3 cleaner).
On heating cycles, the logging works fine, however, when the water heats up to run a hot water cycle, I seem to lose flow measurements towards the end of the cycle once the flow temperature rises above 45C ish. Temperature and electricity readings continue uninterrupted but the flow measurement drops in and out, disrupting the heat calculation and the COP.
This has led me to suspect air in the system and/or cavitation. I’ve got AAVs and have checked the caps on them and those are loose. I’ve checked the bleed valve on the Magnaclean as well though and sometimes it releases water while sometimes it has a foamy gas bubble. I’ve bled the Magnaclean 5-10 times and it seems to be an ongoing issue. The pressure seems to be holding at 2 bar so I’m not sure how air could be getting into the system.
Any suggestions what else might be causing vapour in the system or what else I could try? I’m keen to narrow down the potential problems to something specific I can either handle or hand over to the installer when they come back to do a power flush and snagging.
This will be air in the system. You probably already know how to remove air. You might not realise it yet though. Here’s how I would try to explain it to a lay person.
Imagine that your heating system is a bottle of Coca Cola. It looks innocent enough when it is in the bottle but you just know that it is full of gas. How would you remove it all?
1) Replace the air with liquid. (fill the bottle with coke)
The gas at the top of a bottle is easy to remove. You can open the lid with the bottle standing upright, pour coke inside the bottle, and any trapped gas will escape out of the top.
For a heating system you fill up the system, you open the manual bleed valves / automatic air vents, then you close them when you see liquid coming out.
You have now pushed out most of the “trapped air” (pockets of air that rise to the top of the system) by doing this.
Keep the fill loop connected but switched off. We will need it later for refilling the system and don’t want to introduce extra air when we do.
2) Close the lid, shake it up, then open the lid again. (coke becomes Guinness becomes coke)
If you shake up a coke bottle all of the “trapped gas” becomes “entrained gas” - small micro bubbles that move along with the liquid - even if you are trying to pour that liquid downhill. (watch a pint of Guinness settle)
If you let the coke bottle sit then “entrained gas” will slowly rise to the top again and become “trapped gas” again.
We can use this trick to “move” any “trapped air” that was in places we couldn’t let it out into places that we can let it out.
Bring the system fill pressure up as high as you dare. (e.g. 2.5 bar) This will squash these air pockets into as small a space as possible.
With the system still cold flick the circulator pump on and off (maximum or zero speed) to move stir this air up then let it settle out in the high spots. This is trying to drag the air from trapped places (e.g. a pipe in the attic, where the flow moves quickly like a Mentos dropped into a bottle of coke) to somewhere that you can vent it out (e.g. a radiator, where the flow moves slowly like a pint of Guinness on the bar).
All the radiator valves should be fully open* to maximise the flowrate, and the diverter valve should be switched from heating to hot water and back for this process. Many heat pumps have a “purge cycle” or “venting cycle” that will do this pump on/off and diverter to heating / hot water for you automatically.
Keep running around all our high spots venting any trapped air until the cycle is over.
*If you know the layout of the system you can try to close valves and flush the air out of it “one part at a time” - this will increase the speed of the water in the pipes - but shouldn’t be needed unless you are working with “ceiling drops” or similarly awful pipe layouts that really don’t want to move the air downhill.
3) Boil it off (the cook off)
Even though you have removed the “accessible / trapped” air, and you have also moved the “inaccessible / trapped” air to somewhere that it becomes “accessible / trapped” air so that you can remove it, there is STILL going to be some air in the system.
That glass of coke, bubbles slowly rising to the top, for a very long time.
You can make the process faster by (1) REDUCING the pressure (liquids under lower pressure cannot dissolve as much gas - bubbles only come out of the coke when you release the pressure by opening the lid) and (2) HEATING it up (hot liquids cannot dissolve as much gas as cold liquids - this is why everybody sees the meters warning you about air in the system during last part of the hot water cycle)
You need to reduce the system pressure as far as you can (this varies depending on the height of your building, but something like 0.7 bar should be safe) and then “cook off” all the dissolved gas by running the system as hot as it will possibly go (for an hour or so) and then release this form all the usual places.
Top up the system again when you are done. Now (and only now) remove the fill loop.
4) Microbubble deaeration (optionally - add mentos to the coke)
There might still be some gas dissovled in the liquid. If it comes out anywhere, it will be where the temperature is the highest and the pressure is the lowest. You can help it come out by creating places for the bubbles to “nucleate”, collect into a pocket of “trapped gas”, and then release it.
If this were a bottle of coke you’d throw in a mentos. Here’s a Mythbusters link to break up all this text:
Glycol was pure water is a little like diet coke vs coke. The glycol is gloopier (for google translate users: stickier) and more likely to retain the microbubbles than the regular coke.
If this is a heating system you can add a microbubble deaerator. (sprivovent etc) This should be placed at the hottest, lowest pressure, point in the system.
This is probably one for the plumber rather than the eight year old! They might not be keen on leaving the cap off the deaerator in case it dribbles / leaks later. Best to leave the cap open when setting up the system, and to open it periodically, but otherwise leave it shut.
5) Check water quality
The air NEEDS to be out to avoid mixing with iron and forming rust sludge etc; not just for the heat meter to work correctly.
The water quality also NEEDS to be decent to avoid fouling/corroding your expensive new installation that is expected to last at least a decade.
Professional installers will check water quality; particularly after the “cook off” when the water might have picked up not just dirt but also any salts / nasties that might have been in an old system.
Professional heating system checks (e.g. if you are paying for an annual service package) should also include water quality checks.
6) Check the homework
If you install your OpenEnergyMonitor heat meter / monitor BEFORE the system is commissioned, then you will be able to see exactly when the installer did step 1 (first filled it), step 2 (ran the purge / venting cycle), and step 3 (ran it as hot as it would go for an hour)
I would DEFINITELY recommend this when working with a “high street” installer where the site teams are under time pressure from management and cutting corners won’t be noticed until years down the line. At this point it is too late to conclusively say whether or not it was the initial installation at fault and it will be down to you to foot the bill.
Credits
Thanks to @glyn.hudson and Adam Chapman for the conversation about getting air out of systems last week.
I said I’d have a go at explaining it if they didn’t have time for a video. I’m kinda hoping for something ludicrous involving clear pipes, radiators, and coke…
In the meantime here’s the slightly meaner version of mentos in coke along with some youtube science.
On top of the “how to clear air” instructions I would add that this cleaner is possibly slightly acidic to help clear scale (which will generate gases) or possibly slightly soapy/sticky (which will tend to keep microbubbles and bits of dirt/muck floating in the water as you would hope for cleaning out a system) Either or both would make life difficult for deaeration. Check back once the system is properly flushed / refilled / deaerated I’d suggest.
interesting, thanks, did you find you randomly had gas building up after hot water cycles (I suspect the temperature has something to do with it)?
I’ve got the final stage of commissioning due tomorrow with power flush and dosing the system with inhibitor.
Do you have particularly hard water? I wonder if the cleaner is causing some kind of reaction to the sludge but just keeps up building gas in which case, there might be a good reason to let it keep doing that, unless the reaction is eating away something it shouldn’t!
Thanks Marko that’s a really in-depth response! I’m familiar with water treatment for industrial processes and steam cycles, although domestic dosing seems to be a bit of a black box. I’m inclined to agree the most likely remaining conclusion I have is that the cleaner is doing something to cause gas to form, which doesn’t re-dissolve once the system stops (so it’s not cavitation).
I know the automatic air valves are in the right place and functioning correctly because I tested them by nipping up the red caps and when I loosened them after the next hot water cycle they let out a bit of gas. The majority by far always seems to accumulate in the Magnaclean though.
My water is very soft around 30-40mg total hardness and it’s only dosed with chloramine, this is a pretty standard arrangement in Scotland where I am. I suspect, however, the very low buffering capacity of our water is not so helpful.
I’ll mention it tomorrow that I keep having to de-gas the system time after time and the amount coming off isn’t decreasing every time, hopefully that disappears after the water’s been replaced.
Apologies if it sounded like egg sucking in that case!
It does re-dissolve when the system cools (this is why the first part of the hot water cycle is ok); but it drops out of solution (and forms micro bubbles) as the system heats up and the capacity of the water to retain dissolved air reduces.
Magnaclean, with system stationary but hot, will allow microbubbles to become a large bubble at the top of it. Ditto radiators and other low-velocity high spots. If you try to bleed air off the entire system “one magnaclean at a time” (0.5 litres?) you’ll be there forever (system volume 150 litres?) - it will need to be done at the rads etc with the system hot was above.
30-40 mg total hardness sounds lovely vs the 300-400 mg elsewhere!
Update since it’s been a few weeks - the installer was really puzzled too, they looked around to double check the installation was OK which it is. The flush seemed to (mostly) clear it up; I can now get through hot water (and a rather extravagant couple of days heating cycles due to the Octopus price plunges last couple of days) cycles without losing the flow measurement.
There has been a bit of air when I bled the Magnaclean the other day to check but it doesn’t seem nearly so bad.
I have instead moved on to another issue I’m not sure how to fix with the electricity meters which I’ll post about separately.
