Inexplicable humming (am I going crazy?)

[Yung_hummer]

Hi All!
Bought a house recently, and we have been having the most frustrating issue with a very loud humming noise that intermittently comes and goes in our pipework. Have had a plumber around to check the issue to no avail so far, unfortunately.

We have an Ideal Logic+ c35 combi boiler. System is very new (last two / three years) and all radiators (bar the two bathroom towel rads) are fitted with bi-directional TRVs. Seems that the TRVs are mostly installed on the return side, but would have thought that was fine with a new bi-directional TRV. House has 8 rads + 2 towel rads, about half of them kept to 0 as we don't use all rooms much I'm the house.

The sound seems to come about in the evenings once the system has had some time to run. A low humming begins to build up in one corner of the house that gets louder and louder until it overtakes the sound of the TV. This generally only happens in one corner of the house, and although I am definitely not sure, it seems to only be coming from the return side of the rads on one side of the house.

I can immediately stop the noise, strangely, by going to any TRV (at least the ones I've tried on the 1F) and turning up the TRV to open it (e.g. from 0 -> 5). Turning the TRV back down immediately introduces the sound again at the same volume. Sometimes if I quickly switch the TRV on and off several times, I can get the sound to stop.....until the next day. Its driving us crazy!!

I have tried bleeding the top floor radiator, which does seem to rather easily trap air. Seems to make no difference. I have also tried ensuring pressure on the system is low (about 1.1 bar cold right now). Nothing seems to work.

Any ideas? No one has been able to solve it for us yet, and it's driving me mad!

 

[Ben-gee]

Turn the pump speed down, or has the plumber tried this?

 

[ShaunCorbs]

There not bi directional trvs are they mounted vertical or horizontal for them to be on the return they need to be horizontal eg flow into the head eg like this unless there a danfoss brand

 

[Yung_hummer]

As its a combi with integrated pump, I'm not sure you can? Am I wrong about that? Not sure that the plumber tried at any rate, as I didn't think that was possible. Diving into the digital settings, there was an option for pump modulation, which I have now toggled off (it was previously on) to see if it has any effect.

 

[Yung_hummer]

TRVs are fitted like this, so counter to what you suggested. Will have to double check they are on return, but I do think that's the case. I thought those with double direction arrows were OK with being on flow? Either way, what is weird is that the sound seems to depend on if one is open, not all.

 

[ShaunCorbs]

Common misconception and common noise either humming or loud banging when the trv shuts or opens

Take all trv heads off for a few days to confirm if no noise there’s your problem easy ish fix

 

[Yung_hummer]

So do you recommend I drain the system to remove all of them? Seems like a simple enough job, if a bit time consuming. I don't have lock shields to place in absence which I would need to buy and fit for 8 rads to test - feels a little bit overkill, but maybe you're right? I suppose I could alternatively just refit onto the other side of the rad and see what happens.

Either way, with that many rads looks like I would def need to drain down... - slightly daunted as I haven't done so before, but feels like too simple a thing to pay someone else to do

 

[ShaunCorbs]

I would try removing the trv heads to confirm

Yes to swap they would need draining down and either putting horizontal or moving to the flow side

 

[Chuck]

Worth checking the TRV manufacturer's instructions but the OP's photo in post #5 looks like a bi-directional TRV to me so they should be okay on flow or return side and I doubt they're the root cause.

The radiator that has most influence on the house thermostat should not have a TRV on it, which is not how you have described your system. This needs to be corrected and might cure the problem.

Also, IIRC, your boiler must always have either (a) an always-on radiators sized and balanced to dissipate at least 10% of the minimum boiler output, which I think is 740W for your model or (b) a correctly adjusted external auto bypass valve.

I'd want to check that the pipework is properly supported and clipped.

 

[Yung_hummer]

Thanks @Chuck

That's a really useful observation. I supposed my system is a bit odd come to think of it. All rads bar the towel rads in each bathroom have a TRV, although between the two large towel rads, I would assume there's 740W between them.

The house does not have a thermostat, as there wasn't one installed when we bought the place, and I haven't seen much value in installing one if I have thermal zoning control in each room via TRV (particularly if i want different set temps in each room). Are you saying this is an arrangement we should not have in the house? Is the fact that the entire house is reliant upon TRVs for temp control an issue?

I suppose it does seem to be the case that as all TRVs close, because there is no thermostat to stop the call for heating, the system is effectively just running a continuous loop through the towel rads only.