1/2 inch hot from combi for mixer valve?

[destro404]

Hi! I have found this place in my desperation of googleing for info.

To paint the picture...

Apparently we have a 1/2 inch hot water pipe from our combi boiler. Our bathroom guy says this should be 22mm. He says the fact that it is 1/2 inch the whole way means it is high in pressure.

Our cold water feed is 22mm and is gravity fed from 4 floors up, again the pressure is very good here. His plan is to then drop this down to 1/2 inch as well.

He has his reservations about a mixer shower as he thinks 1/2 inch all the way from the boiler might be iffy. Is this a valid point and would we be better just going for an electric shower? (which I am a bit reluctant to do as I don't think we would then get the full benefit of our good pressure).

Furthermore, do you know of mixer valves which would suit our circumstances? Something that would accept 1/2 inch hot and cold and would be able to cope with a likely pressure difference between the two?

Any other general comments or suggestions are very welcome.

Here's hoping all of my questions are sensible ones and thanks in advance to anyone who takes the time to respond.

 

[ChrisR]

we have a 1/2 inch hot water pipe from our combi boiler. Our bathroom guy says this should be 22mm.

For what reason?

1/2 inch all the way from the boiler might be iffy.

Not a boiler man, then. Combis have flow restrictors in them, which control it to about 10 litres/minute. Far more restrictive than a few metres of 15mm pipe.

Are you suppying cold to the combi from roof tanks? If so why? Can't you use the mains?
If you have to use the tank, check the boiler spec. 4 floors = only about 1 bar.

 

[sooey]

Half inch hot pipe is normal off a combi, tell your bathroom fella to feed the mixer shower cold off the mains, not from the upstairs tank.

 

[destro404]

we have a 1/2 inch hot water pipe from our combi boiler. Our bathroom guy says this should be 22mm.

For what reason?

1/2 inch all the way from the boiler might be iffy.

Not a boiler man, then. Combis have flow restrictors in them, which control it to about 10 litres/minute. Far more restrictive than a few metres of 15mm pipe.

Are you suppying cold to the combi from roof tanks? If so why? Can't you use the mains?
If you have to use the tank, check the boiler spec. 4 floors = only about 1 bar.

Right I think my lack of expertise may be confusing things a bit.

The 1/2 inch (I'm now guessing it is actually 15mm) that comes from the boiler. Are you asking why it is like this? Answer: no idea, it just is. Whoever put the boiler in many years ago did it this way. Or are you simply implying that 15mm from combi boiler isn't a specific problem?

The cold I think is just my fault for being a bit confused, sometimes the bathroom guy's terminology is off - referes to an electirc shower as a power shower, and referred to the water as gravity fed. But I am pretty sure now that the cold is actually just the mains, but starting off on the 4th floor to service all the flats above.

 

[twgas]

if main feeds top flat first it must be overhead mains,
wouldnt be surprised if it freezes all winter

 

[destro404]

if main feeds top flat first it must be overhead mains,
wouldnt be surprised if it freezes all winter

Seems to have worked ok so far this winter!

All I really know is that the cold is the little pipe next to the big waste pipe that comes in through the ceiling and runs down to the floor. When he was mucking around with stuff he had to turn it off outside in the street so I can only presume it is the mains then.

So what I have got from this so far is that my combi is normal and so is the hot pipe coming from it, good to hear!

The thing that throws me slightly is that fact that my other half bought a shower valve which has now been deemed unsuitable - it needs fitted in a cavity which we don't have! the other thing about this valve though is that it has 22mm inlets for hot and cold. Our guy being very warranty-centric said this wasn't a goer either. Do I need to be careful to buy something that suits 1/2 inch / 15mm or was what we bought just a bit naff?

In practical terms are 15mm and half inch interchangeable? Although I'm pretty certain it will be 15mm, it is Vokera which is European right? And not very likely to use imperial measuremnts I would have thought.