TRVs on Combi system - bypass? Drainoffs?

[fathertobe]

Sorry. Amateur question here.

I'm replacing old rads with new 'uns and TRVs. The boiler is COMBI (Valliant) but I can't find a drainoff anywhere. A few questions:

1) Should there be a drainoff or can I do it directly from the boiler?
2) Should I fit one (or more?) drainoffs? If so, better to the lockshield or directly on the pipe is ok?
3) Do I need one normal valve or some kind of bypass valve to ensure everything works properly?

Finally, there is a thermostat in one of the rooms, but I'm pretty sure it doesn't work properly.

Ok, I might be out of my depth here so before I call a plumber, any advice is appreciated... So at least I know what I'm talking about.

 

[Softus]

1) Should there be a drainoff yes or can I do it directly from the boiler? not very effectively, if the rads you're removing are lower than the boiler.

2) Should I fit one (or more?) drainoffs? yesIf so, better to the lockshield or directly on the pipe is ok? It's up to you as to which looks nicer.

3) Do I need one normal valve or some kind of bypass valve to ensure everything works properly? Yes - either or those options

Finally, there is a thermostat in one of the rooms, but I'm pretty sure it doesn't work properly. Oh.

Ok, I might be out of my depth here so before I call a plumber, any advice is appreciated... So at least I know what I'm talking about.
So, you're about to call a plumber then?

 

[fathertobe]

Thanks Softus. You're really kind. This site (and its participants) has helped me enormously this morning.

I'm getting conflicting advice on fitting a bypass or one normal valve. Some people say that TRVs can be fitted to all radiators without a problem.

A web reference would be fine if it's more obviously explained elsewhere.

Thanks again.

 

[Softus]

I'm getting conflicting advice on fitting a bypass or one normal valve. Some people say that TRVs can be fitted to all radiators without a problem.

The best advice I can give you is to suggest that you [always] consult the boiler manufacturer's documentation - this will tell you whether or not a bypass is needed.

If you can't find it then post the Vaillant model here and someone will help you out.

 

[idealmaint]

I'm getting conflicting advice on fitting a bypass or one normal valve. Some people say that TRVs can be fitted to all radiators without a problem.

A web reference would be fine if it's more obviously explained elsewhere.

Thanks again.

I had a conversation with corgi technical a couple of by months back about the need to fit a bypass. I was informed by the tech guy that all systems must have a bypass fitted. If the manufacturers said that the bypass fitted on the boiler (if fitted) was sufficient then that would satisfy corgi but not the building regs which he said needed a separate auto bypass.....this could not include a radiator with no TRV because this could be shut down


Again this is just what i was told by corgi. On the few new boiler I have fitted i have included one rad with no TRV (in room with stat) and an AUTO bypass

 

[chrishutt]

Vaillant combis have an integral automatic by-pass and do not require an external one. However you should not fit TRVs on all rads. One space (hall or lounge) should have a room stat (working!) and no TRV on the rad.

 

[fathertobe]

Thanks for ALL your advice here.

In the end all rads got fitted with TVRs as thermostat isn't working. It's a Vaillant Combi so no bypass either.

We will get there in the end...

 

[kevindgas]

the answer to the problem is that a room stat is required under part L of building regs trv's should be fitted to all living areas as a minimum but a bypass can be either an automatic one about £18 - 20 or a radiator capable of handling the boilers output on shutdown usually about 3000 watts with both lockshield valves fully open and no wheelhead just 2 blank caps

hope that helps

 

[chrishutt]

Kevindgas, the point has already been made that since the boiler has a built-in by-pass he doesn't need an external one. As for the permanently open rad acting as a by-pass, what difference does it make how many Watts of output it has? Surely any size rad would would do just as well.