TRVs not fully open at maximum?

[mrbrunes]

Hi

A friend has an issue with her downstairs rads not reaching full temp, so after some basic diagnosis (bleeding rads, refilling system) I found that by unscrewing the knurled ring on the TRVs and removing the top part that the rads became fully hot. This was rather a surprise to me as I thought that the most anticlockwise position (or specifically the 'V' marking on the Caleffi TRVs) was fully open. I've swapped several around and they all exhibit the same behaviour. As I unscrew the knurled ring I can hear the water flow entering the rad, even when the TRV is on max. The valve pins all seem to move freely. I checked the Caleffi site but their support docs page is 'Not Found' .
Are TRV thermostats interchangeable i.e. can I just swap the top part for another make?

Is this normal? If so then do I need to increase the flow/pressure of the system somehow?

 

[Agile]

Most are NOT interchangeable.

Are you sure the valve body is correct for the head?

Sometimes, a TRV will have an adjustment available which might be incorrectly set.

Just a make does not identify an exact valve, most have several different models.

Tony

 

[WLF85]

Most TRVs I've tried are complete rubbish.

In my current property I spent 450 quid on 9 Arroll TRVs. They are beautiful to look at but perform poorly as TRVs.

Even when fully "open" they regularly close prematurely as stay closed for hours, even with a cold room and a cold radiator.

I complained to Arroll and their technical team responded to inform me that I needed to fit the TRV away from the radiator. Unbelievable.

 

[mrbrunes]

Tx for the info. Will try to find the exact model and see if there are any adjustments. It's a newly purchased house and having see the prev occupant's handiwork I wouldn't be surprised if the valves didn't match the bodies!
I have a spare Honeywell which I will try to screw on to see if that makes any difference.

 

[D_Hailsham]

So your friend is complaining that the rad is not very hot. This could be because the room is up to temperature and the mechanism in the TRV head has closed the valve down, restricting the flow through the rad, which will cool down. The rad should now be giving off just enough heat to maintain the required room temperature. Think of a TRV as like a cruise control. You set the temperature and the TRV adjusts the rad output (flow rate) to reach and maintain the desired room temperature.

The important thing is: does the room reach and maintain the required temperature? If it does, there's nothing to worry about.

 

[WLF85]

He already said the TRV is fully open. Most TRVs when fully open should stay open until around 30 Celsius.

I'm guessing his room isn't getting up to 30 otherwise he wouldn't be posting here with this problem.

 

[mrbrunes]

Exactly, the rooms are not reaching the right temp.
Sure I understand how the numbered TRV settings work, but maximum (or 'V' whatever that is) should be full flow, no?

 

[D_Hailsham]

Was the head set to max (V) before it was removed or replaced?

 

[mrbrunes]

Yes, as I said before "As I unscrew the knurled ring I can hear the water flow entering the rad, even when the TRV is on max."

 

[MrTherm]

mrbrunes,

Caleffi trv's have various interchangable heads (as many as 5 types) which is very impressive, however it depends which model you have fitted.

One popular model has a screwdriver blade slot on the number setting rim where the head can be locked in one position or even locked in high to low positions.

It is best to check that this blade slot is in the full adjustment position (in-line pointing towards the head) otherwise it will act as you have described.

 

[Agile]

He already said the TRV is fully open. Most TRVs when fully open should stay open until around 30 Celsius.

I'm guessing his room isn't getting up to 30 otherwise he wouldn't be posting here with this problem.

It is not normal for anyone to want rooms at 30 C and rads are only sized for a room temp of 21 C

 

[WLF85]

Well done Agile for completely missing the point as always

 

[dilalio]

Well done Agile for completely missing the point as always

 

[mrbrunes]

Ok here's some pics of the TRV - no model markings that I can see, just '0811', which doesn't appear to correspond to a model.

As mentioned by MrTherm it indeed has a screwdriver slot to lift up the body and allows you set a different max temp, but this has not been done on any of the valves.
(I did find some Caleffi instructions at http://www.caleffi.com/sites/default/files/file/01034_na.pdf which cover this)

Also after I'd spent some time trying to think of Italian synonyms for "maximum" starting with V, I've just realised that the V marking is not a 'v' it's a roman numeral '5' - doh! I'm just not used to 4 being written IIII ...

Then I tried screwing a Honeywell TRV onto the old body, but this exhibits exactly the same issue, so I can only think that TRVs are not fully open when on max and that there must be some lack of pressure in the system affecting the downstairs rads. Any thoughts on this?

 

[D_Hailsham]

The heads may be Caleffi, but are the bodies?

Are the downstairs TRVs same as upstairs?

Can you post a pic of a problem body, showing any markings?

A TRV should be fully open when the room temperature is more than 2C below the value set by the head. So, with the head set to V, the TRV should be fully open below 26C (V=28C for a Caleffi head).

Is it a sealed or open vent system?

Has the system been balanced?