Noisy trv

[asajoh]

Hi

I'm new here, but I have searched these forums and the internet in general, so I've heard some of the possible solutions to my problem. I suppose this is just to sum up and make sure what I've heard is up to date, as some posts are nearing 10 years old.

I recently (a couple of months ago) had central heating fitted. I have a small combi boiler, 3 radiators and a heated towel rail. The rads have trvs and the towel rail valves are left slightly open at all times.

All the piping is (very noisy) plastic and there is inhibitor in the system. The trvs are bidirectional (two arrows pointing in opposite directions), but I couldn't tell you what make they are.

My problem is with the large radiator in the living room. When it reaches temperature, the trv doesn't shut off, but narrows down a bit slowing down flow. This way, unless I turn the temperature down on the trv, the water never seems to completely stop flowing.

Although I don't know if this is how it's meant to work, it wouldn't really bother me so much if it wasn't because when the trv reaches a certain level of "closedness" the water makes a really high pitched (right at the top of my hearing range) whistling noise as it rushes through the trv. Adjusting the trv up or down stops it until the trv again reaches temperature. I've tried ignoring it for hours at a time, thinking maybe the trv was just in the process of shutting down, but it never stops unless I do something.

The other end of my radiator has a normal valve, as far as I can tell. It has a plastic knob that I can turn to open or close the valve unlike the lockshield valves I see described where you need tools to do it. Adjusting this other valve also sometimes solves the noise problem, but again only temporarily.

I've bled the radiators several times since installation and now only (quite clean looking) water comes out, so I'm pretty sure there is no air in the system.

I recently added some more water to the system (getting it up to 1 bar) because the pressure was a bit low (from all the bleeding) and that exasperated the problem.

I thought maybe the pump was working too hard, but I see no way of adjusting it.

Do I just have really rubbish trvs? (I forgot to mention, the trv on the rad in the bedroom started making a clanging noise when turning on/off until I adjusted the valve at the other end down a bit, thereby I think restricting flow and pressure on the trv.).

 

[D_Hailsham]

I have a small combi boiler, 3 radiators and a heated towel rail. The rads have trvs and the towel rail valves are left slightly open at all times.

Make, model and output of the boiler?

Do you know the total output of the radiators? Use Stelrad Elite Catalogue if you don't know (Use the page headed 50°C.)

Who decided which make and size boiler you needed?

Do you have a wall thermostat?

All the piping is (very noisy) plastic and there is inhibitor in the system. The trvs are bidirectional (two arrows pointing in opposite directions), but I couldn't tell you what make they are.

Noise is due to the speed the water is travelling round the system.

My problem is with the large radiator in the living room. When it reaches temperature, the trv doesn't shut off, but narrows down a bit slowing down flow. This way, unless I turn the temperature down on the trv, the water never seems to completely stop flowing.

That's how a TRV is supposed to work. When the room is cold the valve will be fully open when the room is up to temperature it will closed down just enough so the output is just enough to maintain the required room temperature. It's like the accelerator on a car: you press it down to accelerate from 0 to 70 and then have it nearly closed while maintaining that speed.

when the trv reaches a certain level of "closedness" the water makes a really high pitched (right at the top of my hearing range) whistling noise as it rushes through the trv. Adjusting the trv up or down stops it until the trv again reaches temperature.

Cause by the high speed of the water.

Was the system balanced?

I thought maybe the pump was working too hard, but I see no way of adjusting it.

Pumps are often not adjustable on combi boilers. That's why I asked which one you have.

 

[asajoh]

The boiler is a Main Combi 25 Eco (25 kW output)

The link that you gave me didn't work, but I can tell you that I calculated a need for about 16000BTU (I make this about 5kW, just quick estimate) all in all for my rads and the ones I have fitted are the sizes to supply about that.

I spoke to a few different plumbers before having the boiler fitted. They recommended approximately 25.

There is no wall thermostat, no.

All the piping is (very noisy) plastic and there is inhibitor in the system. The trvs are bidirectional (two arrows pointing in opposite directions), but I couldn't tell you what make they are.

Noise is due to the speed the water is travelling round the system.

Actually, the noise is the pipes expanding and contracting, which makes them rub against their fastenings. It was very disconcerting at fist because it gave a tapping noise, almost like water dripping. There were no leaks, though and eventually I realised that heat expansion/contraction was the cause.

Good to know the trv is doing what it's meant to. That's a start

No, the system wasn't balanced. I've considered this, but it means going out and buying thermometers (which, of course I will do, if you lot think that would really solve this). The rad with the noisy trv is the furthest from the boiler and I've heard the other valve should be kept fully open on that rad.

Oh, and I should mention that the plumbers have fitted all of the trvs on the return end of rads as far as I can tell (they warm up on opposite end to trv first). I hear that doesn't really matter with modern bidirectional trvs, though.

 

[D_Hailsham]

The link that you gave me didn't work, but I can tell you that I calculated a need for about 16000BTU (I make this about 5kW, just quick estimate) all in all for my rads and the ones I have fitted are the sizes to supply about that.

Sorry about the link; Stelrad have changed their website. Here is the correct link: Stelrad Elite Catalogue. Use the page headed 40ΔT. This is because your boiler works with a 20C difference between flow and return.

The boiler is a Main Combi 25 Eco (25 kW output). I spoke to a few different plumbers before having the boiler fitted. They recommended approximately 25.

That boiler has a minimum output of 7.6kW so, assuming you are correct about your rads, it is massively oversized for heating. It is probably correct for hot water as installers tend to size combi boilers just on the HW requirement and completely ignore the CH requirement.

There is no wall thermostat, no.

It's a requirement under Building Regulations; the installer ought to be aware of this. Ask him why he did not include it in his quote.

The room where the wall stat is located should not have a TRV on the radiator.

Actually, the noise is the pipes expanding and contracting, which makes them rub against their fastenings.

Interesting

No, the system wasn't balanced. I've considered this, but it means going out and buying thermometers (which, of course I will do, if you lot think that would really solve this). The rad with the noisy trv is the furthest from the boiler and I've heard the other valve should be kept fully open on that rad.

You can do a basic balance just by feeling the pipes; hot on the flow, cooler on the return. Remove all TRV heads and set all lockshield valves to half a turn open from fully closed. Feel the return at the boiler so you know what you should be aiming for. Any rad with a hotter return pipe should have the LS valve closed an eighth of turn; cooler return, open an eighth of a turn. Wait 10 minutes between adjustments. Get all rad returns as near to the boiler return, but don't expect perfection.

What temperature do you have the CH set to on the boiler?

It doesn't matter which end the TRV goes if it is bi-directional.

 

[gsplum]

Oh, and I should mention that the plumbers have fitted all of the trvs on the return end of rads as far as I can tell (they warm up on opposite end to trv first). I hear that doesn't really matter with modern bidirectional trvs, though.

I did read once that there is a theoretical argument about locating the TRVs on the return so as to minimize temp reading error from the hot 'flow' pipe but in practice it really make very little difference.

 

[asajoh]

Sorry about the link; Stelrad have changed their website. Here is the correct link: Stelrad Elite Catalogue. Use the page headed 40ΔT. This is because your boiler works with a 20C difference between flow and return.

Ah, I looked in the catalogue (I managed to find it) and that's where I found the 5kW, but that wasn't based on 40 Δt (not sure which one I used). At 40 it comes to more like 4.6.

That boiler has a minimum output of 7.6kW so, assuming you are correct about your rads, it is massively oversized for heating. It is probably correct for hot water as installers tend to size combi boilers just on the HW requirement and completely ignore the CH requirement

Yeah, looks like it. Not sure what to do about that, as I hope to use hot water for the shower when I have my bathroom done (have an electric shower now). Probably wouldn't be much good for that with a smaller boiler, right? Should I get more radiators? (trying to think where to put them in my extremely small flat.)

It's a requirement under Building Regulations; the installer ought to be aware of this. Ask him why he did not include it in his quote.

I had no idea. I don't like wall thermostats, so didn't ask for one. I would have, had I known I had to have one. (I grew up with central heating with trvs but no wall thermostats. They seem like an unnecessary extra to me, but that's probably because I don't understand what they're for.)

What temperature do you have the CH set to on the boiler?

It's at 60 degrees at the moment, but I used to have it at 40 before it got cold. I imagine, seeing as it is over powered, I should keep it at a lower temperature?

 

[asajoh]

Oh, and I should mention that the plumbers have fitted all of the trvs on the return end of rads as far as I can tell (they warm up on opposite end to trv first). I hear that doesn't really matter with modern bidirectional trvs, though.

I did read once that there is a theoretical argument about locating the TRVs on the return so as to minimize temp reading error from the hot 'flow' pipe but in practice it really make very little difference.

I also heard the trvs are better angled away from the rad, as they always are in my neck of the woods, but here they always seem to be in line with the rad (and on my rads, at floor level. What's that all about apart from making people hurt their backs trying to adjust their trvs?)