Balancing CH with Smart TRVs

[ringzer]

Hi,

I'm sure balancing CH systems has been asked millions of times and I've read and followed many guides on how to do so but still struggling with heating our loft.

Problem:
Radiators in the loft are only getting luke warm

Background:

1. We live in a typical semi-detached house with a loft converion (so ground floor, first floor and loft).
   
2. Ground floor heating is UFH controlled separately
3. System is unvented and boiler is Worchester Bosch Greenstar 30CDi Classic System and hot water is MegaFlo
4. Boiler is running now and temps is 61C and pressure is just above 1 bar
   
   
5. Radiators on the first floor and loft.
   
6. Ground and first floor was installed 9 years ago and is working great - plenty of heating coming out of the radiators
   
7. Loft was added 4 years ago and since then we've struggled to properly heat the loft
8. To avoid running a separate flow and return from the boiler to the loft (would have required extra chasing), the plumber suggested we "T" off the first radiator in the system in the main bathroom to extend the system into the loft.
   
   
9. The loft radiators (there are two - one in each bedroom - loft is about 25m2) are single vertical radiators
   
10. There is a towel radiator in the bathroom which doesn't have any clear valve and lockshield valve and doesn't have a Tado Smart TRV (I read at least one radiator should not have a smart TRV to avoid the system overrunning if all TRVs were off)
    
11. If I open both valves on the towel radiator, it heats up to the point of being too hot to touch.
    
12. For the loft radiators not heating, the lockshield valve is opened fully and I have put back on the manual TRVs and put on max but still only lukewarm.

To improve any fluctuations in the output of the radiators (particularly the larger ones on the first floor) I added Tado Smart TRVs to all radiators. This works great for ensuring radiators are turned off when the temperature is reached and having quite granular heating patterns.

However as mentioned the radiators in the loft are only getting luke warm. I have tried balancing the system with limited success and have bled all the radiators.

Questions:

My specific questions are:

1. What impact if any does the "T"-ing off the first radiator have on throughput to the loft, if any?
   
2. On the towel radiator, which value is typically which? How can I check? I haven't found anything online.
   
3. What can I do to ensure the loft radiators are heating fully, especially when all other TRVs are turned off via Tado so all heating should be pushed to the loft.
4. What lockshield setting should I have on the radiator in the main bathroom (point 6 above)? Enough to just heat that radiator or more to allow more flow to get to the loft?
5. What lockshield setting should I have on the loft towel radiator? If both valves are off would that impede flow to the other radiators? I suspect the towel radiator is not before the radiators and if it was as I've had both valves on the towel rail off before (as we don't use that room) the other radiators would be stone cold.
6. Is it possible that the system pressure of just over 1 bar (still in the green range) is a contributing factor? I doubt it is, as the towel radiator in the loft gets very hot. Should I top up the pressure - I think it gets done by opening both ends of this flex to let water through for a period. System was only serviced in Oct 21 so plumber would have ensured that was at the right level.
   

 

[BlueLoo]

Are the tall rads plumbed in the correct flow direction? (check Manf bumf).
Do you have a vented central heating system

 

[ericmark]

I am not a plumber, but did have problems with my mothers house, I read all the instructions, but if you break one rule, likely you also need to break another to correct it.

Boiler is standard boiler (not condensing)

That is the bit which may change things. Mothers house had a condensing or modulating boiler, so the boiler would always be running.

I know one should use a differential thermometer to set the lock shield valves, but could not find it, so started by turning off each lock shield valve waiting for pipes to cool, then ¼ turn at a time back on until just a little warmth in feed pipe.

This resulted in all radiators working, but what I then realised was speed is critical. It takes around 3 minutes for the TRV to move from fully open to fully closed, if in that 3 minutes the radiator gets stinking hot, it starts a hysteresis so it is important no radiator heats up too fast.

The TRV shows current and target, as does the wall thermostat, the aim is to ensure current does not exceed target, clearly at times the current will be below target, and once the rooms where current exceeds target are trimmed, you may need to open those below target a ¼ turn.

But adjust rooms which are over temperature first.

The DHW is my problem, it is thermo syphon so in the summer it only runs 20 minutes before the return water turns off the boiler, but in the winter the return from the DHW is turning the boiler off before the radiators are hot. Well maybe not the DHW, all I can say is hot water returns before all radiators are hot.

Ideal would be a by-pass valve so when the TRV's close the by-pass opens, but pump is on my return, so by-pass idea will not work, my bathroom radiator is thermo syphon so not having a TRV on bathroom radiator does not stop the pump sucking on closed TRV's. I just cross fingers and hope when warm enough for all TRV's to close the wall thermostat will turn off.

 

[ringzer]

Are the tall rads plumbed in the correct flow direction? (check Manf bumf).

I assume so - how do I check. Not sure what you mean by Manf Bumf

Do you have a vented central heating system

Unvented system I believe - updated original post.

 

[oldbutnotdead]

I assume so - how do I check. Not sure what you mean by Manf Bumf


Unvented system I believe - updated original post.

Manufacturers installation instructions.
Teeing off that 15mm isn't ideal but it should have enough thermal capacity to run 3 rads. Of course if the bathroom rad is itself teed off a 15mm leg that gets more interesting...
Do you know how convoluted the run to the loft rads is, are there any kinks and sharp bends likely to be airlocked thus reducing the flow to upstairs?

 

[ringzer]

Manufacturers installation instructions.
Teeing off that 15mm isn't ideal but it should have enough thermal capacity to run 3 rads. Of course if the bathroom rad is itself teed off a 15mm leg that gets more interesting...
Do you know how convoluted the run to the loft rads is, are there any kinks and sharp bends likely to be airlocked thus reducing the flow to upstairs?

What I can't understand is the towel radiator in the loft gets too hot to touch where as the vertical radiators in the loft are luke warm, sometimes a bit hot but not hot all over.

The pipework from the first floor to the loft should be very straight forward - no obstructions to get around etc.

I've tried bleeding the loft radiators and water comes out. Is it possible water could come out first and then some air? Do I need to bleed for longer maybe? Just dont want a wet floor...

 

[oldbutnotdead]

First thing to do is find the manufacturer's info for those vertical rads and make sure they've been plumbed in the right way round (there are internal baffles so it does make a big difference). After that start looking at more subtle stuff.
By the way, don't assume that because you paid someone to fit them they will definitely have done them right- everyone makes mistakes!

 

[ianmcd]

shut off all rads except the loft ones and see if they then get hot

 

[ringzer]

shut off all rads except the loft ones and see if they then get hot

So you mean shut off the TRV or lockshield valves?

With the smart thermostat system, Tado, I can control when the TRVs are on and off. Typically during the day when I'm working from home so others TRVs are off and just the loft is on (and just luke warm)

 

[ianmcd]

So you mean shut off the TRV or lockshield valves?

With the smart thermostat system, Tado, I can control when the TRVs are on and off. Typically during the day when I'm working from home so others TRVs are off and just the loft is on (and just luke warm)

no need to touch the lockshields just close them all down with the trv

 

[ringzer]

no need to touch the lockshields just close them all down with the trv

I'm afraid I've already done that and I get luke warm rads.

 

[ringzer]

First thing to do is find the manufacturer's info for those vertical rads and make sure they've been plumbed in the right way round (there are internal baffles so it does make a big difference). After that start looking at more subtle stuff.
By the way, don't assume that because you paid someone to fit them they will definitely have done them right- everyone makes mistakes!

The installing plumber was competent and no concerns. But I've also had my very competent plumber who services the boiler every year check it out a while back and nothing untoward was found.

Would having them installed the wrong way around make them work badly or not at all?

These are the radiators https://www.traderadiators.com/trade-direct-nevo-designer-radiator-white-1800mm-x-272mm The documentation doesn't suggest any way round for installation, but the TRV is on the left which matches the photo on the page.

The radiator is 2,000 BTUs which might be a little under spec'd but only a couple hundred BTUs. I guess my main problem is I can't even heat a slightly small radiator, so the size of the radiator for now is a moot point.

 

[ringzer]

Also, I've realised my towel rail has two manual "lockshield-type" valves. When I turn them both to the max, the towel rail gets very hot. But if I want to set it to pass through a reasonable amount of flow (given it's quite far from the boiler at this point), how do I know which to open maybe half way?

 

[ianmcd]

teeing off from an existing radiator, to feed those designer radiators, was always going to be a bit hit and miss

 

[BlueLoo]

Also, I've realised my towel rail has two manual "lockshield-type" valves. When I turn them both to the max, the towel rail gets very hot. But if I want to set it to pass through a reasonable amount of flow (given it's quite far from the boiler at this point), how do I know which to open maybe half way?

Open the inlet fully.
Open the out 1/2 turn only.