Air getting into upstairs radiators. Possibly caused by kettling?

[nick_a_louse]

I need some help from the internet before I waste any more time and money trying to fix air getting in to my central heating! Looking for advise on what to do next, as the 3 plumbers I've used so far haven't been much use. Down in East London, near Romford for what it's worth!

Issue summary:

• Boiler is a Vaillant ecotec 837 plus, I imagine over 10 years old (we've only been here 6 years). Heating set to 70 degrees. It's in the loft conversion (so top of the house).
• All radiators get hot, but the red radiators (See diagram below) are affected by the sound of noise air passing through the valves. Air accumulates but isn’t hydrogen (passes the flame test). Most of the piping is copper, except the loft conversion.
• The downstairs yellow radiator makes a gurgling noise but air doesn’t get to it. Isn’t airlocked - gets hot.
• If all / most of the TRVs are open, then the rads are basically quiet as you would expect. During the day, it's likely that just 3 radiators are on (Office, + 2 in the conservatory).
• I noticed last week that you can hear (what I assume is) kettling in the boiler. I was under the impression that kettling didn’t produce significant amounts of air in the system. Maybe air being pulled in somewhere else and passing through the system?

I think this is roughly how the plumbing is - hard to tell as I haven't lifted all the floors. Laid out as ground floor, first, second.


Things tried (in rough order) to stop the noise:

• All radiators and TRVs replaced in the last 6 years
• Boiler serviced annually, currently no leaks, magnaclean cleaned (and never particularly bad after 12 months)
• Replaced a leaking diverter valve in 2019; plumber speculated it was damaged by the particles flying around the central heating.
• Power flushed in November 2020 after towel rail / last rad replaced. Used chemicals, they went around banging the rads, added inhibitor afterwards
• Got the AAV replaced in March 2021 out of desperation during a service (thought air might be being sucked in. We removed a piece of scale or rust lodged in the pump impellor too.
• Have tried the various pump speeds in the service menu (no change)
• Last plumber adjusting the diverter value (no change)
• I’ve gone around and checked for any leaks in rads / visible piping. Pinched a couple of nuts.
• Got a sieve fitted on the return feed, incase the powerflush somehow missed particles making noise. Came out empty after a few weeks though so I’ll probably remove the sieve insert at some point.
• Last time I checked, pressure is~1.5bar at 32 degrees C, ~1.9 at 70 degrees. Doesn’t appear to fluctuate significantly. Not many opportunities to recheck the pressure at cold temp now it’s winter.

Help please!

 

[John.g]

If you reduce the boiler temp from 70C to 60C does the noise die down?.
Is it a combi boiler.

 

[John.g]

Also have a browse through this, system was changed from OV to sealed and noise still persisted until boiler temp reduced from 70C to ~ 65C or <. Don't know if solution to problem was ever found but a few suggested that the boiler HX might be the culprit, also one suggested that too much inhibitor could cause foaming at higher temps leading presumably to pump cavitation etc.

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[nick_a_louse]

If you reduce the boiler temp from 70C to 60C does the noise die down?.
Is it a combi boiler.

Yes, it's a combi boiler.

Dropped the temp to 60 - wife said it was a little quieter in the office but still makes noises. My normal measure is when it wakes me up at 6am, so I'll report back tomorrow with my relative findings.

 

[John.g]

You might post the location of the ecotec 837 plus's expansion vessel relative to the pump, ie on the pump suction side or the pump discharge side if you come across a schematic in your users manual.

 

[nick_a_louse]

Also have a browse through this, system was changed from OV to sealed and noise still persisted until boiler temp reduced from 70C to ~ 65C or <. Don't know if solution to problem was ever found but a few suggested that the boiler HX might be the culprit, also one suggested that too much inhibitor could cause foaming at higher temps leading presumably to pump cavitation etc.

Thanks for the link - It's entirely possible that too much inhibitor has been added - I've ordered a testing kit, since it's less than £6.

I guess there's no way to actually test if the heat exchange is damaged / blocked with out destructively testing it. I did wonder if it could be blocked with rust or scale particles though (as some were quite large).

I'm loathed to chuck another £200-£300 at the problem, but unless someone else chimes in then I might just bite the bullet!

 

[nick_a_louse]

Also have a browse through this, system was changed from OV to sealed and noise still persisted until boiler temp reduced from 70C to ~ 65C or <. Don't know if solution to problem was ever found but a few suggested that the boiler HX might be the culprit, also one suggested that too much inhibitor could cause foaming at higher temps leading presumably to pump cavitation etc.

Am I right in saying this would be the main (massively expensive) heat exchanger, not the smaller rectangular one?

 

[John.g]

Am I right in saying this would be the main (massively expensive) heat exchanger, not the smaller rectangular one?

That's correct, the rectangular one is a water to water Hx that provides DHW. I suggested in the link above....

"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."

That could be relatively easily done in the above case as the pump was external, In your case, you cannot easily do this because the pump is integral with the boiler so obviously can't circulate around the system with the boiler isolated but would need a external circ pump but I would certainly consider it as you can buy a cheap throwaway 5 or 6 meter pump on ebay for £50/£60, if you could install this yourself + the by pass then you can take away all the guesswork re the boiler causing the problem, (and that's what I would probably do)

With the existing system You may be able to switch the circ pump on "manually" from the boiler menu to circulate water through the system (and boiler) with the burner off which may tell you something?

 

[nick_a_louse]

"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."

Sadly, the boiler still makes quite a racket in the morning at the reduced temperature.

Thanks for all the suggestions the additional feedback. Time, and the horrific location of the boiler (above, but perpendicular to the stairs to the loft conversion) stop me wanting to get involved with hooking up an external pump etc. I imagine you can do it by removing a rad and Heath Robinson-ing it, but I'd still want to wait until warmer whether arrives.

The service / installer manual doesn't seem to have a dedicated 'circulation pump run mode', but there is a 'mimimum burn test mode' which is probably the closest I'll get to running the circulation pump on its own - I'll give that a whirl and see what happens to any noise. This location is the same reason I'm desperate to avoid a new boiler.....

Unless the above test mode reveals something definitive, I'll suck it up and wait until spring. More options available when there aren't a cold wife and kids around! I have a feeling that a £600 bill is in my future though.

 

[John.g]

Could you (if installed) extend the pump overrun time to say 5 minutes, shut the ABV (if installed) and then open the zone valves manually once you shut the boiler down??.

You can set it all right but if you do decide to do the test ensure all air is vented first. It actually defaults to 5 mins but you can extend that to 10 or 15 minutes to do every thing at your leisure.
All you have to do after extending the overrun time is to ensure boiler running then turn roomstats down, the burner will stop firing and pump overrun commence.

 

[nick_a_louse]

Could you (if installed) extend the pump overrun time to say 5 minutes, shut the ABV (if installed) and then open the zone valves manually once you shut the boiler down??.

You can set it all right but if you do decide to do the test ensure all air is vented first. It actually defaults to 5 mins but you can extend that to 10 or 15 minutes to do every thing at your leisure.
All you have to do after extending the overrun time is to ensure boiler running then turn roomstats down, the burner will stop firing and pump overrun commence.
View attachment 73026

So I was finally able to get some time to play around with the boiler (set the overrun to 10 minutes).

After a short period, the radiator was quiet, and no kettling-like noises from the boiler (just the hum of the pump).

So my understanding is that the water continues to flow as normal during overrun, to help draw heat out of the heat exchange etc. I guess this rules out air ingress through the pump etc, and makes the main heat exchange the only remaining candidate. Correct?

Anything else worth considering before I start looking at quotes? Still going to be cheaper than a £2-£3k for a new boiler + labour

 

[John.g]

Presume you manually opened zone valve(s) once pump overrun commenced? If so, would possibly point to Hx problem, if so, unlikely to be scaling problem as it's the primary Hx, partial blockage, unlikely, maybe inhibitor causing problems? Just dont know. You could just drain the whole system down, refill, do not add inhibitor and see if problem persists. When (if) you do this and if problems the same, suggest giving Vaillant a tincle and see what they say, they may have a fixed price for Hx renewal, the fixed price might also include a general boiler check out.

 

[nick_a_louse]

Presume you manually opened zone valve(s) once pump overrun commenced? If so, would possibly point to Hx problem, if so, unlikely to be scaling problem as it's the primary Hx, partial blockage, unlikely, maybe inhibitor causing problems? Just dont know. You could just drain the whole system down, refill, do not add inhibitor and see if problem persists. When (if) you do this and if problems the same, suggest giving Vaillant a tincle and see what they say, they may have a fixed price for Hx renewal, the fixed price might also include a general boiler check out.

Re values during pump overrun - yes, I popped off the TRVs to ensure they stayed open.

I managed to find time over the weekend to drain everything down (except one rad with a seized drain point). Refilled with no inhibitor, but so far it seems just as noisy after 24 hours.

I had a look on the Vaillant website, they seem to outsource all their servicing to third parties (one of the 'MasterTechs' has actually already been here, with little helpful advice except to do another power flush). I'll try and call Vaillant, and see if they have anything else to offer.

Thanks again for the suggestions- will update this thread, in case someone else has a similar problem!

 

[John.g]

Only other items that may cause noise are the TRVs, some makes like Tower seem particularly noisy but some of the better known ones have caused noisy operation as well,I have mine installed horizontally on the rad returns so the water flow is from under the valve seats, bi-directional are supposed to operate in either direction.

If you have a schematic of your boiler, you might see where the expansion vessel is installed, ie, before the circ pump or after it, if no schematic ask the installer, you can,t do anything about it in any case, shouldn't matter as long as the E.vessel pressure is 0.75 bar or greater when cold which yours is.

If the boiler CH temp is set to its minimum of 35C/40C, is it still noisy?.