New heating system - TRV Confusion

[WELLY417]

Hi

Installing a new combi system but a bit confused over TRV requirements. I believe the usual practice is to fit TRVs to all radiators except one, which is fitted with fully open lockshield valves on both flow and return to make sure there is always an outlet for the boiler. I'm also told this is usualy the main hallway radiator and /or where the room thermostat is.
Just wanted to check:

1) Anyone see anything wrong with the above before i start?

2) Towel rail valves - most of them for sale seem to be standard rather than thermostatic. I also think the standard ones look better but i'm not sure if they are ok to use? (not sure if regs are involved here, or if its ok to mix normal valves and TRVs in the same system?)
Also, if ok to use, do i then treat the towel rail as the 'boiler outlet' and fit a TRV in the hallway? (plus where would the best place for the room stat be with a setup like this)

Thanks in advance for any help

 

[gas4you]

My understanding is that your first statement is correct, although it doesn't have to be the hallway. This is just the traditional place rather than the best.

I always fit trv's on towel rails, but others on here are of the opinion that the rules on trv's are only 'guidelines' rather than regs written in stone.

I can see their point, its really a matter of how you read them.

 

[Agile]

If its a complete new system then you have to fit an auto bypass valve and TRvs on all rads except where the room thermostat is located.

Its more usual now to fit the room stat in the living room as hall temperatures tend to reflect more how often the front door isn opened than the temperature in the rest of the house.

Tony

 

[WELLY417]

Thanks for the help
Bit lost with the auto bypass valve Agile mentioned though. Can anyone explain?
Also, could do with a recomendation for a decent looking chrome TRV for a towel rail - like i said, have only been able to find non thermostatic chrome valves (makes me wonder why this is if new systems need to be be all TRVs?)

Thanks again

 

[giblets]

I think that Drayton do a fully chromed set of TRV & lockshield valves for towel rails. Mind you, the price is

 

[gas4you]

Pegler do one I believe, ask at your local Plumb Center.

An auto bypass is needed to comply with latest regulations. This will open to allow flow through boiler if all the trv's shut.

The Vaillants I fit have this built in, but as you are having one rad without a trv I would not worry on a combi system.

 

[Doctor Drivel]

Pegler do one I believe, ask at your local Plumb Center.

An auto bypass is needed to comply with latest regulations. This will open to allow flow through boiler if all the trv's shut.

The Vaillants I fit have this built in, but as you are having one rad without a trv I would not worry on a combi system.

The flow through the one rad may not be high enough and by-pass valve must be fitted.

 

[gas4you]

The radiator that has no trv should in theory be about 10% of the heating load.

As said the Vaillant's built in one is fully adjustable and therefore you do not need an external one.

 

[namsag]

Most new combi`s have a built in bypass and manufacturers instructions usauly don`t ask for any other bypass but as g4y says the rad left without trv should be enough with its pipework if extra is req .. Some standard boilers with flow switch fitted are saying in instructions that no by pass is req.

 

[WELLY417]

Just got boiler manual out which says 'appliance includes an automatic by pass valve which protects the main heat exchanger...... if system includes TRVs and / small bore it may be necessary to fit an external by pass to facilitate correct operation of the boiler'
Bit confused now - does the rad without TRV qualify as an 'external by pass' as mentioned?
Going back to the towel radiator thing. have found some old threads where it has been recomended to use towel rail as the outlet with no TRV. Anyone got any thoughts on the pros & cons of setting up like this? Seems like an easy solution but would this mean room stat needed in bathroom (which would not strike me as a great idea?)

 

[gas4you]

Can't have room stat in bathroom as no touchable electrics are allowed in there.

If you must then have towel rail and hall rad (or whatever) without trv, but then won't conform to regs fully.

I think you are looking too deeply into this and worrying unduly