Why is UFH design and boiler choice so difficult? ATAG, Veissman, Vaillant and the need for buffer tanks

[Adsibob]

I'm having a bit of a mare. Signed a contract last year with my contractor to basically do everything. I provided a fairly detailed draft spec for the UFH design and boiler and cylinder choice. I specified a multizone UFH system throughout the house, plus 3 towel rail heaters, a Veissman Vitodens 200-W system boiler, a 300L indirect unvented hot water cylinder made by brand recommended here and Tado controllers.

 

Although Veissman has had mixed reviews here (e.g. here) it consistently gets well reviewed elsewhere and is the Vitodens 200-W is simply the most efficient gas boiler on the market. It modulates much better than any other boiler, with a modulation ratio of 1:17. My understanding is that this means you can fire it up to output 1/17th of its maximum output, which makes it quite good for heating water to the lower temps that UFH require efficiently. By comparison, the modulation on a Vaillant is only 1:5 or possibly 1:6 on some models. I specified Tado because I've used them before and my wife and I were really happy with them. We had some of the kit already so thought why not expand that system.

 

Since we signed the contract I've been reminding the contractor that he needs to introduce me to his heating engineer so that we can go over my draft spec. Initially he admitted he thought I had had a professional design it because it was so detailed. He was surprised i did it myself and reluctantly agreed that we would have such a meeting. That was months ago. He then spoke to his engineer who explained he was not approved to install Veissman so I wouldn't get the 10 or 12 year warranty. He is registered with Vaillant and Keston and possibly one other. I had a look at Keston and wasn't impressed. Not sure why. I am familiar with Vaillant and never had particularly good experiences. They're okay, but their main appeal is that when they break down there are plenty of people who can fix them. I don't see that as a good USP. It's backwards thinking. One is better off buying a boiler that is more reliable. In addition to the great reviews for Veissman, I noted that their website actually promotes Tado products, which I thought was a bonus. 

As I've still not met my builder's engineer and as the UFH installation is scheduled to be start in the next couple of weeks, I started to worry. A friend put me in touch with a local plumber and heating engineer who she raved about. Looking at his website, he seems to have plenty of great reviews. 

 

I called him up and he said that whilst he can fix most boilers, he prefers to install Veissman or Atag. So big tick from me. I know Atag is not that well known here in the UK (at least according to this post here) but this engineer liked them. However, for my situation he recommended Veissman. Only issue is that he's not too keen to do the job as doesn't want to take work away from someone who is already on site. Fair enough I suppose. He was very helpful and offered to talk through my system with me. Surprisingly, he advised against having so many zones and said instead I should have only one zone per floor, and try and keep the temperature stable given the long response times. If installed this way, with the Veissman controlling most of the heating requirements, including its weather compensation feature, then it wouldn't short cycle and I wouldn't need buffer tank. If however I wanted so many zones, then he would recommend a 300L buffer tank. Not sure I have space for that and also I don't understand why it needs to be so big.

 

So now I'm more confused than ever. I know Vaillants are popular here, but really concerned about their efficiency/sophistication. I think they are an okay mid range boiler, but prefer something more premium. If I were to go with my contractor's engineer and accept Vaillant, what's the best way to ensure they run efficiently? Low loss header or buffer tanks? If buffer tank, how big? My property will need the following floor spaces heated by UFH, 81m2 ground floor, 55 m2 at first floor and then about 30 m2 in the loft. It is fairly well insulated, but nowhere near passive standards. Does it matter where the buffer tank is?

 

[TonyT]

Fitted a vitodens combi in the in-laws house 2 weekends ago, great boiler

 

As they are getting on, we just used the existing 230vac stat and programmer, as they were getting worried about a new one.

 

so plus one for vitodens from me!

 

 

[ToughButterCup]

The problem you have is not specific to plumbing or heating. The issue is generic.

 

In this sector, its  hard to compare like with like. To the conversation add the sound of axes being ground,  personal preference, petty fogging nit picking, and you have the most common self-build problem: lack of sleep due to an overloaded brain.  Picked your windows yet? If you have, you'll know what I mean. If not, prepare for another round of wailing and gnashing of teeth. 

 

Sleep well.

Ian

[TonyT]

Oh and for £180 you get a full 10 year warranty complete with parts and labour 

[Adsibob]

39 minutes ago, TonyT said:

Oh and for £180 you get a full 10 year warranty complete with parts and labour 

Do you know if the installer needs some sort of Veissman approved certification to get that, or could my builder's gas registered engineer install it and I still get the warranty by paying that?

[TonyT]

Will find out tomorrow!

[TonyT]

He is Viessmann registered and has to be Viessmann trained to get onto installers portal to enter the data for the warranty.

[TonyT]

Oh and it’s a 12 year warranty not 10.

[Adsibob]

2 hours ago, TonyT said:

He is Viessmann registered and has to be Viessmann trained to get onto installers portal to enter the data for the warranty.

Thought as much. Would he do a job in London? if so, can you PM me his details please?

[TonyT]

Doubt it, it’s a 10 hour drive.?

 

maybe the viesmann website will have a list of local installers?

[Adsibob]

1 hour ago, TonyT said:

Doubt it, it’s a 10 hour drive.?

 

maybe the viesmann website will have a list of local installers?

It does, but so far the two guys I contacted are possibly cowboys.

[SteamyTea]

You mention 'engineer' several times in the introduction.

 

I suspect the best you will get is a technician.

 

(this is not to demote technicians, they are skilled people, but they should not be promoted to engineer status without the proper higher education qualification)