House replumb, new combi, lose the cold water storage

[ALEC1]

There in lies the rub..no one really knows how the 470 will work with a manual blending valve for UFH.. the big issue is the relation between a call for heat from the UFH and the compensated temperature that the boiler is working at...

the optimal solution is to use an electronic blender with the VR 68 mixer module...but the valve and motor alone will set you back £250...then there is the pump and the module itself...

The mixer module and the vr 470 allows the system to work with compensated flows..and that means you wont go running around turning things on and off...the way we love to in the UK..it all becomes intervention free..

If it were me I would install a pipe in the bathroom floor as if it were UFH and allow the compensated flow from the boiler to circulate with no controls other than two valve, or if you wanted a TRV... no costly manifolds, NO costly UFH controls and NO separate pump...

As compensated flows settle at about 40-50c, then it doesn't necessarily need to be mixed. But beware if the compensated flow goes up so will the floor temperature...you can over come this with a pipe stat and two port valve. alternatively you could just set the boiler maximum to say 60c

Heat input into floors is limited to avoid damage...

 

[RussTaylor]

Thank you very much for explaining all that.

Ok, as the cost of doing it the more technical way looks like it'll be at least £1200 for my little bathroom it just isn't worth it.

A electric system is the cheapest/easiest bet, just be nice to have the floor warm in the mornings when we shower, this would do that fine. The cost of running an electrical one looks cheap as well (about a tenner a year I think for 1 hour each morning).

As this is my first major plumbing rework I'm a little worried about more experimental UFH systems, as I really don't want to spend money and not like it or have to keep having the floor up until I get it right. Also if it causes an early death to my boiler I'll beat myself up about it for life.

I want a great install, set and forget like you say. I'm sick of super hot radiators for a few hours each day and the missus letting all the heat out because it's too hot.

I'll go electric if I have to I think, as it'll probably just be on for an hour every morning and maybe I can pop it on manually if I need to. I'm sure if I get a decent electric kit the controls will be ok. I might just get the heat lamps though, I really like them but I don't think it'll help our floor.

Appreciate your time going through this with me, next house when I've got the money I'll do something more fancy.

Thank you.

 

[RussTaylor]

Hmmm back to the 937 and UFH, after a lengthy email with questions, Vaillant technical support said this

"Thank you for your email.

It will be fine to use the 937 but we don’t recommend using Vaillant controls where there is underfloor on the system.

Regards"

Which is incredibly helpful. From what I've learnt doing this will make for a rubbish install with a very hot floor?

Ho hum... the warmup electrical UFH system looks alright

 

[ALEC1]

No its not very helpful..but it can be done with their controls...

I agree its a funny old world where a manufacturer doesn't want to sell their products...

but even with numpty on-off controls its questionable wether a small zone of UFH for a bathroom with wet UFh is worth the investment...

 

[ChrisR]

you wont go running around turning things on and off...the way we love to in the UK..

Nobody goes running round turning things on and off. Alec likes to make up this sort of thing rather a lot.

Get three quotes!

 

[RussTaylor]

Thanks guys.

Well whatever I get will be a step forward. I think you're right, electric is the way forward and much more within my capabilities / budget.

Does anyone fancy taking a look at my diagram on page 3 please and see if you think the layout makes sense? Basically all CH on 22mm pipe teed off in 15 per radiator. 15mm for all water around the house, running seperate circuits from the boiler for each area.

Thanks again!

 

[ALEC1]

Smaller pipes equates to faster delivery times of hot water but can compromise performance if the taps are not flow regulated and the pressure inadequate...


much like heating I would run 22mm to a room and then branch down to 15mm to the outlets...you would never or very rarely fill a bath when you are running a shower...etc, etc

 

[ChrisR]

Alot of my clients

That's odd, I certainly don't "regularly" touch mine, and neither does anyone I know of with a normal correctly installed system.

I don't know how ( or IF) you're measuring supposed under or overshoots, I get about half degree.
Why call that "numpty"?

While here - Alec said there was legislation which said we had to have boilers capable of having compensating controls connected.
But it's easy to buy one where that doesn't apply.

 

[RussTaylor]

Ok that makes sense, I think I half thought that. I only want to buy decent taps so I'll look out for flow regulation.

I agree, as I think this through there is little that will be happening simulataneously.

The boiler output is 15mm for HW, should I step it up to 22 to the room and back down to 15mm? Some rooms only have one hw out so I guess stick to 15.

Cheers

 

[ALEC1]

I would take 22m right up to the boiler and then out of it too..and tee off to each outlet in 15, up to the bathroom which can all be done in 15..

15mm has a signficantly higher pressure drop than 22, and 22 holds more water so you wait longer at the taps...its a bit of a balancing act...

if you are going for the 937 don't forget the blender..

chris numpty as in they do one thing only, unlike compensation controls which to what on-off controls do and much more...

its not a reflection of the installers in the industry..but seeing as compensation controls are widely available in europe, its more a reflection of the sales people of big companies like honeywell that describe them as complex.. compensation controls are not complex, they just do more! For this reason honeywell do not supply them in the UK

 

[ChrisR]

SO you're talking about one independent control manufacturer, when it comes down to it, and NOT of all boilers, which you stated.
How many countries in Europe insist on compensating controls?
Is it the one you keep mentioning before and told not to -?

If you mean simpler say simpler - "numpty" is derogatory and misleading.
I repeat - half a degree.

And do remind the good folk of the other side of "simpler" - controls which swathes of installers and users shun, for very good reasons you never mention.
You get a lot of stuff wrong and it's all in one direction.

Original Poster - get three quotes!

compensation controls which to what on-off controls do and much more...

More? Except in many cases, they don't react to an internal temperature being too high or too low.
If you're interested in people complaining about that, one place you find it is on German forums like this one. But I don't think you are interested.

 

[RussTaylor]

Hi, sorry, three quotes for what? I've had five plumbers come around to replace my boiler and even British Gas didn't check my water supply. I've got a friend who will do the connection/commissioning/gas/paperwork and check I've not made a screw up and the rest I can do myself.

Look, fight as much as you like but I'll be having the 470 controller as I like the idea of it potentially running more efficiently. I'm sure all options have their pros and cons but even my forty year old system had an outside thermostat.

Anyway back on topic, seems daft the boiler has 15mm DHW connections when I'll be going to 22 and presumably most people will do.

Thanks for all the help, I think I have a workable plan now, just need to double check my water mains dynamic pressure and flow rates Very much appreciated, this forum and you guys are a god send

 

[ChrisR]

Sorry Russ, many of us (apparently) are uncomfortable when Alec pushes a particular line, with, as above, errors & omissions, to put it politely.
What I mean is it's up to you of course, don't let any one person drown you in their pet approach.

Couldn't agree more that there are many pretty awful plumbers out there.
From your approach, I think you'll be able to make good decisions for yourself.
Good, experienced plumbers would all do things a bit differently from each other. There's only so much info you'll get on a free internet site.

 

[ChrisR]

Flow rate - 20 litres/minute causes a drop of about 0.5 metres per metre run in 15mm copper. 22mm is about 6x less.
(Depends which table you look it up in though...!)

 

[RussTaylor]

I don't doubt a quality plumber (one who cares about it rather than sees plumbing as a means to an end) would do this and more for me, and have experience to call upon. Sadly I can't afford one or don't have time to seek out a good one so it's down to me

I suppose everyone has their own experiences and opinions, it's nice to hear a variety of views and draw my own conclusion. This forum is good for that

Well I'll aim for what we've discussed then, it's easy to think that 15mm is just a fraction smaller than 22mm, but it's not when you're talking area and fluid dynamics. I'll start pricing up 22mm then

Thanks again, I'll be back when my gf has another bright idea or I've struggled with my 937 install