TRV in the same room (Hall) as room stat - is it always a bad idea?

The rad in the same room as the room 'stat should really not have any other way of having it's temp individually regulated - there would likely be a conflict. This rad-and-room-'stat-combination is what sets the boiler balance for the whole house.

In practice, it'll probably be ok, but it isn't ideal. So, imo, it's best to disable this TRV.

You can then ensure this large rad doesn't heat up the hallway at the expense of the rest of the house by doing just as you suggest - turning down the other end of the rad which should be a 'lockshield' - ie: a conventional rad valve that you set and then leave alone.

The TRV end should be disabled - simply turn it open to 'max', and perhaps slacken off the head part too chust to make sure.

It'll then be a case of balancing this hallway rad so's it gives out the required amount of heat for the hall whilst the rest of the house keeps up.

What temp would you like the hall to be - 18oC? If so, set your room 'stat to this, and if the hall gets too hot too quickly so's it turns off the 'stat before the rest of the house gets warm enough, then simply tweak down the hall rad lockshield a wee bit so's its output is reduced slightly - it'll give out its heat more slowly, which will allow the rest of the house to 'catch up'.

Once the hallway and the rest of the house are happy, then you've found the right 'tweak'.

(If you have a working TRV on the hall rad, what could happen is: hall rad comes on full, hall gets hot, TRV turns the rad off before the hall 'stat is triggered to go off, rest of house gets too warm. It'll probably be 'ok', but it isn't ideal - there should only be one 'system' controlling the overall house temp. Obviously, the TRVs in the other rooms are a good idea. The room 'stat basically keeps the boiler going at the correct rate - supplying enough CH water, but then turning itself off when not required. With a purely TRV-controlled system, the boiler will only shut off when it's internal water gets too hot.)

 

If you dispense with the TRV on the hall radiator, it could have the opposite effect. Hallway being a smaller room than others in the house , could switch the thermostat off a tad early. As Teuchter says, it's a matter of trial and error to get the balance right.

 

I have asked a similar question recently and got good advice from teuchter. Removing the TVR from the radiator in the room where the Room Thermostat is located will resolve the problem.

I still have some tweaking of my system to do, but it is running fine and the house is warm.

An alternative suggestion that I heard from my local plumbing merchant was to fit an Automatic Bypass Valve to the system, in combination with an External Temperature Sensor.

This setup does apparently allow for TVR's on all radiator. Unfortunately, I am not very experienced and didn't understand the principle exactly.

From what I understood the Automatic Bypass Valve acts like an always on radiator in the system.

Perhaps someone with experience will explain how this setup works.

 

Hmmm, I don't understand that either

As far as I know, an automatic by-pass allows water to continue flowing around the system even if all the rads (TRVs) have shut off. This is largely to protect the boiler/pump. Usually it is pressure sensitive and only allows by-pass when the rest of the system has closed and the pressure then increase - you don't really want it allowing water to flow willy-nilly from the flow to the return of the boiler; that would be a waste, and would keep the return temp higher than needed - not good.

By not having a TRV on a rad, this does the same job as an auto by-pass.

Most modern boilers have one built-in too, as a safety thingy.

The external temp sensor is a different beast. This will automatically keep your condensing boiler at it's most efficient by modulating it down as far as it can whilst still providing enough CH. You want the return temp as low as possible, so that's what it's designed to do.

A useful addition, I think.

But bu@@er all to do with anything else.

As far as I know...

 

If the TRV is set to 20C and the wall stat to 22C the rad will shut off at 20C and the boiler will keep running and running as the temperature will never rise to 22C.

If the wall stat is set to 20C and the TRV to 22C, the wall stat will turn the boiler off at 20C. The TRV will never operate.


Why are you installing a much larger radiator? If it's because the current one does not get the hall up to temperature, you should not have any problems and should not put a TRV on the radiator. If you find that the hall now heats up too quickly, so the wall stat turns the boiler off before the TRVs in other rooms have worked, just close down the hall rad a bit at a time, so it gives off less heat and then turns off last.

 

as an auto by-pass.

Not quite the same job. You still need an ABV, even if you have a rad without a TRV. This is because the pressure in the system will increase as the flow rate reduces due to the TRVs closing. The flow rate could drop below the minimum stated for the boiler and the increased pressure could either make the TRVs work incorrectly or produce noise in the system, e.g chattering TRVs.

 

I didn't understand what the guy in the plumbers shop was telling me regarding Auto Bypass Valves and External Temperature. Partly because I have no experience of them, and partly because the guy was Dutch and I am not.

I have studied a schematic diagram of this layout, and I can see how it assembles, but I still can't figure out how it works. Unless the external temp. sensor overides the room stat.

The diagram definitely shows an Automatic Bypass Valve fitted to the pipework of a system using my model of combi (Nefit Topline Compact HRC 30/cw5).

The boiler is new and modern (I hope), but if it had a built in Automatic Bypass Valve, why would it need a second one on the pipework.

As I said, I don't really understand this, which is why I took the advice of teuchter and removed the TRV from the radiator in the room with the room stat in it.

However I would really like to understand how it works. At the moment I am just really happy to have a working system and a warm house, but I would like to look at ways of improving the system when the summer comes.

 

Twuncat, Sam Spade's explanation of the reasoning behind not having TRVs and room 'stats in the same room is clear and concise (the b'st'rd...). So, hopefully, that bit is clear.

The external temp sensor has nothing to do with the room 'stat - the room 'stat simply monitors room temp and shuts off the boiler when it's reached.

The external temp sensor ('compensator' I think it's also called?) controls the boiler temp output. Modern condensing boilers have 'modulating' burners which means the flame doesn't just come on FULL like old boilers, but instead can vary just like the burner on your hob. This means it can keep the output temp as low as it can get away with - and the lower it is, the more efficient the condensing boiler operates.

If you don't have one of these fitted, for max efficiency you should instead manually turn the boiler CH output down as the weather warms up.

Whether to fit a by-pass valve, I can't really comment. Personally, if it were mine, and if I had a main rad with the TRV disabled, kept the output temp as low as possible, and the system worked fine without any weird bangs, rad valve chatter, etc, then I wouldn't bother fitting one.

But that's not a pro opinion...

 

But that's not a pro opinion.....................No, but always worth a read.

 

Teuchter, Same Spade may be concise, but I already understand this part thanks to you replying to an earlier post of mine.

I am now a lot clearer on the external temp sensor, thanks. I asked again at the plumbers shop, and you are spot on. It does exactly what you say, and I will be fitting one

My confusion seems to have stemmed from studying the schematics for this type of setup. It turned out that I was just examining one example of how my system could be arranged. I must have got over excited because it shows all radiators with TVR's.

As for the Bypass Valve, again I am going to take your advice and leave it. Perhaps only if it increases efficieny would I look into it further.

But the system is working well now, and there are no weird noises. I will need to experiment with the boiler output temperature, at the moment it is set low anyway, while I have been ironing out any teething trouble.

Once again, thanks for taking the time to help.
You sure know your stuff if you aren't a pro.

 

Sorry Ricjjhns,

I ambushed your thread there.

However I now know the answer to your question.

Listen to Teuchter!!!

 

The by-pass valve doesn't increase efficiency - it's just to prevent the boiler trying to force water around a system where all the rads have 'closed down'.

Personally, I would take all the 'TVRs' away from the rads and give them all Micras, or your system may run too fast.

 

OK no increase in efficeiency, so that's me sorted then....

or is it?

What are Micras?

Will they involve me removing 500 Euro's worth of TRV's and replacing them with something even more expensive? This isn't a problem for me, as I intend to brag about how much my system cost at a later date.

I am already considering zoning the system in the summer, following your suggestion in an earlier post. That should add to the cost nicely.

 

A Micra is a base model from Nissan. And a 'TVR' is...

(Well, you done the typo first... )

 

You might not be concise, but you are funny.

 

Rick, turning down the rad valve won't increase sludge - but you DO really need to get rid of what's there, and then prevent any further from building up using inhibitor (sludge is corroded radiator innards...).

(Possibly, in theory, a 'trickling' rad valve might make sludge more likely to settle inside the rad, but that ain't the point; the valve WILL need to be shut down a bit, and sludge MUST be removed...)

Best ways to remove sludge is to take off each rad and hose them through. Then add cleaner to the system and run and drain it several times. Or, get it power-flushed. The former you can do yourself if you are reasonably competent, the latter is a pro job (unless you are very competent.)

No harm keeping the TRV on the hallway rad - just make sure it's set to higher than the room 'stat level so's it doesn't start to shut down before it's triggered the 'stat. (Read S Spade's post again.)

If the lounge is the coldest - fast heat losing - room, then that's another reason for putting the room 'stat in there. Once you have the heat level in that room set using the room 'stat, then the other rads in the house can be adjusted to suit the individual rooms. However, I'm sure you can get it all balanced fine with the room 'stat in the hall.

It's never a problem to have rads oversized - they can always be shut down.