House replumb, new combi, lose the cold water storage

[RussTaylor]

Hmmm, I always thought the outdoor sensor was a bit of a gimmick, I actually removed it from my current system as I didn't understand why the outside weather should bring my heating on (it might already be warm inside). I'll do some reading on them, but what is the real benefit?

I figured they'd last as well, if not because they're a 10 year newer design than the ones packing up now.

I'll also figure out what a blending valve is.

I had a shower this morning, I think the 937 despite it's huge size maybe the way forward, 20ltrs/minute for 10 mins would make a good shower, takes 2 minutes to recharge and then the missus can have one.

Thanks for your help, really appreciate all that I'm learning and avoiding making a monumental mistake

 

[RussTaylor]

Hi,

My boiler is about 30-40 years old. I found a box on an outside wall that was unsightly and I thought it was a duff telephone ringer until i took it apart and found a thermostat inside. I figured it was to bring the heating on when it froze or something.

Vaillant say

"With this option, outside sensors measure temperature changes and adjust the boiler performance to maintain the desired inside temperature, allowing your boiler to operate with maximum efficiency. "

I didn't realise you could adjust boiler performance ... so if it's warm outside it won't try so hard and save some gas? Sounds like a no brainer, why don't they all have them? £££ obviously, but it's not much more to add it to an 837/937.

 

[RussTaylor]

Good explanation of weather control further down this page

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=189

Well worth it, and I'll look into Viessman boilers as well, thanks

 

[RussTaylor]

Sorry, just wondering what do I need a blending valve for? To add cold to the hot water feed out of the boiler?

Thank you

 

[ALEC1]

I didn't realise you could adjust boiler performance ... so if it's warm outside it won't try so hard and save some gas? Sounds like a no brainer, why don't they all have them? £££ obviously, but it's not much more to add it to an 837/937.

The blending valve on the 937 (only) allows you to store water at say 70c and blend down with cold to a usable temperature of say 48...Vaillant in the small print do say you should use one, but not in the instruction manual so don't blame the installers!

I have several937s with the blender and they are fantastic bits of kits, with out the blender the shunt pump fails prematurely...you only need to look at the schematics to find out why..

 

[RussTaylor]

Nice to hear a 937 recommendation. I think I am headed that direction although it'll be harder to find space for it. I'll certainly fit a blender, thanks again.

Shame they're not doing the 5yr warranty at the moment though.

 

[ALEC1]

the 5 year guarantee is for a vaillant registered installer...if you use there controls and set it up correctly you are unlikely to need a guarantee...thats true of viessmann too though!

don't forget a system filter though!

 

[RussTaylor]

I've just looked and my outside tap is on a 8-10mm bore extension, so hopefully flow much better when I measure it properly.

I have looked for the Viessmann but they don't seem to be so readily available to buy, and the 222-F is about £900 more than the 937. Probably stick to a Vaillant as they seem easier to find and I presume easier to support?

Thanks again

 

[Agile]

Just did the bucket in the garden ... 11.5 litres / minute.

Thats an open pipe flow rate. Nothing do do with what you will achieve when passed through a combi and a shower head, probably less than half!

Only a dynamic flow rate means anything!

I wonder what conclusion you come to about those people you have had who did not measure it ( or probably even know what dynamic flow rate is? )

Tony

 

[Agile]

I have looked for the Viessmann but they don't seem to be so readily available to buy, and the 222-F is about £900 more than the 937. Probably stick to a Vaillant as they seem easier to find and I presume easier to support?

Thanks again

You should be using a Viessmann registered installer or you may not get the maximum length warrantee They will know where to buy the boilers.

You will find that installers mostly do not like working for anyone who buys the boiler themselves.

In that case you would find yourself dealing with any warrantee issues yourself!

Tony

 

[ALEC1]

viessman 222 is a great boiler...but don't oversize it if you go there... the 19kw boiler gives over 180l of hot water in the first 10 minutes...if you have the flow...

 

[Agile]

19 kW gives about 8 litres per minute of hot water. In 10 minutes that 80 li !

 

[ChrisR]

He's presumably referring to the F which has a 100l store. It's big - a detail left out.

It does always pay to take things some posters say with a bucket of salt.
There's plenty of the usual misinformation & dissembling in this thread.

Original poster - talk to the manufacturers, potential installers and make up your own mind. You already have experience of something NOT doing what some "enthusiastic" brochure-quoting plumber bloke doubtless said it should. An overwhelmingly common tale.
The vast majority of new installations do not have external sensors, for many reasons, some good, some bad. Up to you to decide about that.

 

[RussTaylor]

I've got a plumber already who's happy to do the install/gas safe bit and I can do the donkey work. I will probably miss out on the 5 year warranty but I'll have saved a packet anyway.

Lots to think about, just hope I've got enough flow/pressure

 

[ChrisR]

You shouldn't need to hope - get the plumber to find out, and tell you. If he's not competent to do that, he'll quite possibly screw up the controls installation like the previous guy did - as well. Leaving you down the line wondering why things don't quite work properly and seem to be doing something funny, etc etc etc etc.