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.

 

[Chuck]

Thanks @Chuck
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?

Yeah, what you've got is a legacy from the 1970s and is not how it should be done these days.

I would want to install a central programmer-thermostat, usually in the hallway as close to the centre of the house as possible. This tells the boiler whether heat is needed or not. I like the Honeywell T4R but there are several alternatives, which no doubt others will propose if they disagree with my suggestion. If you use the wireless variant, it's a simple DIY job to install and the receiver replaces the existing time switch, which I assume is what you have now. To a first approximation, if the radiators are sized and balanced correctly then most of the TRV's will stay open most of the time with the ones in rooms that are subject to a lot of solar gain closing to compensate on sunny days.

Since the heating won't be running with all the TRVs closed your pump won't be throttled to the point where your humming / water hammer occurs.

I'd expect installing the T4R to make a noticeable improvement to the comfort level in the house and also reduce the gas consumption associated with heating by 10% – 15%.

I'd also put TRVs on the bathroom towel rails and you need to remove them from radiators in the room where the T4R is sited.

 

[Ric2013]

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

Shaun means the sensor head, for the experimentation, not the whole valve. Which does not involve draining.

If you want to then drain the system and have the TRVs on the flow, you don't really need to buy anything except possibly some new olives for the pipe compression connection as you'd swap the TRV and lockshield on each radiator.

I'm also of the opinion (possibly a misconception if Shaun says so, as Shaun is rarely wrong in fairness to him) that the arrows mean it is bi-directional, but I generally go by the installation instructions. It is worth noting that some bidirectional valves need to be told which way the flow is going in order to work in reverse direction and there is a setting that hasn't been changed because no one read the instructions. I can't find a manual for that valve, but suspect it may be an Altechnic. If it is, it may be worth trying the firms's technical department to find out whether there is an installation manual available, then we'll know.

I wonder if by opening one TRV fully, you are reducing the pressure across another TRV, so it may be worth seeing where the actual noise comes from rather than get hung up on whether opening a TRV stops the noise. When you find the culprit, you may find CLOSING it, as well as opening it, stops the noise. Is it possible that the noise is coming from a particular valve, possibly an old or a faulty one, or perhaps one of them isn't bidirectional?

Sometimes the older valves could be very noisy when holding back a high pressure, for example the early 90's Giacomini TRVs, which is why people are discussing whether there is a bypass to allow flow/reduce pressure when all TRVs are shutting. I'd agree you should have a thermostat to save fuel, but you'd generally have a permanently on radiator in the same room as the thermostat, so, as you have some radiators permanently on already, I don't see what this has to do with the noise your system is currently making: the permanently on radiators you currently have should act as a bypass in that they allow a minimum flow. Now, if ALL your radiators had TRVs on them, then it would be another matter, as you could end up in a situation where the pump is running and they are all nearly closed, but you say that isn't the case.