Separate Zone for UFH on Vaillant system

[Milleniumaire]

I've had a couple of Vaillant registered plumbers look at my system and discuss my requirements. One has recommended installing a bypass valve between the flow and return near the boiler. He did explain why, but I didn't fully understand at the time.

Is this normal? My previous system and current system were not installed with this, so I'm wondering if, after 15 years of not having one, why it is now necessary.

All other recommendations; VR61, VR81 and motorised valve matched my understanding of what was required. It was also suggested that additional valves be installed to allow parts of the system to be drained.

 

[Milleniumaire]

Ah, I've just noticed that in Agile's earlier comment he talked about an auto bypass valve. Obviously, this is what the plumber was talking about and having done some research I can see why this might be needed on a multi zone system.

 

[Milleniumaire]

Either use the individual actuators designed for the manifold or something like guardian solutions smart zone valves.

Hi Dan, the manifold doesn't currently have any actuators and I would need three, one for each of the loops, and as they are heating the same combined area this seems like an expensive way of fitting a motorised valve, so maybe a single valve would be better.

Regarding the Guardian Solutions smart zone valves, was there a particular model? Maybe this one Smartzone 22mm

I notice they sell the header for £2 less than the valve!

I currently have Salus MV222's, which retail for around £56. A couple of years ago I had to replace the actuator head for one of them and it cost me less than half the price. I wonder if this is an indication of the quality of the head?

Although I could leave the decision upto the plumber I want to make sure he uses both a motorised valve and bypass valve that will last.

I know you plumbers - fitting cheap parts to maximise profits and get more work later on (only joking)

 

[Dan Robinson]

Are you subdividing the UFH? Or is it one zone?

 

[Milleniumaire]

The UFH is a single zone.

 

[Dan Robinson]

No these:

http://www.guardianstore.co.uk/heat...es/smartzone-pro-22mm-2p-zone-valve-comp.html

Salus are shyte.


You can't/shouldn't use conventional zone valves with UFH as they can be open for hours and hours.

The one above is based on a UFH actuator so can stay open for days if needed. I've started using them on weather compensated heating as well now for the same reasons.

Had to remove a fair few conventional zone valves due to them being run for too long with UFH in the winter.

 

[Milleniumaire]

Okay, thanks for the link. I'll discuss with the plumber.

What is it about these valves that make them better for UFH. Is it a different design or better materials? They don't look to have a manual switch, but then the only time I've had to use that is when my Salus valve stopped working!

They seem to be a good price as well. Much cheaper than the Salus.

 

[Dan Robinson]

The end switch is in the head. But it doesn't work like a zone valve.

They can be open almost indefinitely without seizing. Hence the head is the same as found on normal UFH manifolds.

If the plumber is the same one that put the system in then I would save time and start bashing your head on the wall now.

 

[hossacd]

Ah, I've just noticed that in Agile's earlier comment he talked about an auto bypass valve. Obviously, this is what the plumber was talking about and having done some research I can see why this might be needed on a multi zone system.

The Vaillant 637 system boiler has an internal auto bypass valve.

The Vaillant controls also start and stop the system in steps so in normal operation the auto bypass valve is not activated as it first opens the zone valve, then starts the pump and a few seconds later starts the burner then when no further heat is required it stops the burner leaving the pump on overrun and a few seconds after the pump stops it closes the zone valve. With non Vaillant controls the zone valve closes first so the water during the pump overrun needs to run around the flow/return via the auto bypass valve. Auto bypass will still operate if you have no radiators without a TRV or a fault occurs with the zone valves.

 

[Milleniumaire]

Dan, the plumber isn't the same guy who installed the system. I got some names from the Vaillant Registered installers web page.

hassacd, if the 637 system boiler has an internal auto bypass valve, I guess that suggests one doesn't need to be fitted outside of the boiler.

I can see in the installation manual it states:

3.11.2 System by-pass
An automatic system by-pass is provided in the boiler.
The boiler is suitable for use in systems with
thermostatic radiator valves and no additional by-pass
is required. The by-pass valve is adjustable, see section
5.3.

Thanks for the information, I'll pass it onto the plumber. I can't help wondering if he should have know this?

 

[Dan Robinson]

The internal bypass on a lot of boilers is not meant for the system - purely the boiler.

If the Bunny book says it is OK, then fine.... a lot of internal bypasses wouldn't be enough to stop problems with TRV chatter.

 

[hossacd]

Thanks for the information, I'll pass it onto the plumber. I can't help wondering if he should have know this?

When I was getting quotes only one installer knew the boiler had an internal auto bypass the other 2 I got quotes off didn't and wanted to install an external one. All were Vaillant advanced installers so I was a little surprised they didn't know.

 

[Dan Robinson]

Becoming Vaillant Advanced doesn't take very much.

 

[Milleniumaire]

The internal bypass on a lot of boilers is not meant for the system - purely the boiler.

If the Bunny book says it is OK, then fine.... a lot of internal bypasses wouldn't be enough to stop problems with TRV chatter.

Had a chat with the plumber and he thinks installing an external bypass valve would help but agreed it isn't necessary. I also called Vaillant Technical support and discussed with them (for what it's worth) and they were fairly sure an external bypass wasn't necessary.

Given that I've had no issues with the current setup I'll probably NOT bother with the external bypass. Of course, there's always the possibility that the extra load on the system from the UFH will cause issues, but if that does happen it's easy enough to add it later. If this did happen, maybe I would consider a LLH!

 

[capri]

Hi Milleniumaire

It is possible to know what the final solution was/is on your installation?

Thanks