setting of auto bypass

[eagleeye]

I am in the process of renewing all the pipework in a customers property as the concrete has corroded it. I fitted a new boiler there almost a year ago and converted from open vent to sealed system. Now due to a number of leaks in the concrete floor i am renewing. As it is a big house i am removing the 2 shower pumps and fitting an unvented cylinder. Both the boiler, cylinder and controls will be in loft. I did fit a auto bypass the last time but never set it up properly. Can anyone tell me what setting it should be on ?? It is a Vaillant 438 with a grumfos 25/55 pump. In total the system holds about 300 litres

 

[Mike Jackson]

The instructions that came with it will tell you how to set it up. You can't just set them to a setting you have to adjust them in situ.

 

[eagleeye]

Thanks Mike, yes I understand that they have to be set whilst in place. Just seemed like there was a particular setting for a particular boiler and pump

 

[PETE 123]

I dont bother with auto bypass they dont always work after a while i stick to a gate valves

 

[lame plumber]

I dont bother with auto bypass they dont always work after a while i stick to a gate valves

have a look at building regs if your signing off work in your own name

 

[helpsy]

I think the regs say 22mm auto bypass valve to be fitted

 

[chris watkins]

I think the regs say 22mm auto bypass valve to be fitted

They do, under Part L only auto bypasses should be installed so that hot water from the flow isn't fed straight back into the return, raising the temperature & taking the modern boilers out of condensing mode.
But that is not what eagleeye is asking, he wants to know how to set his one up, so come on all you heating guys, help him out !! tell him how you set yours up.
He has a 438 which needs a min of 27.2 L/M (1633L/h to give a 20deg drop @ 38kW)

 

[Rickster123]

They do, under Part L only auto bypasses should be installed so that hot water from the flow isn't fed straight back into the return, raising the temperature & taking the modern boilers out of condensing mode.
But that is not what eagleeye is asking, he wants to know how to set his one up, so come on all you heating guys, help him out !! tell him how you set yours up.
He has a 438 which needs a min of 27.2 L/M (1633L/h to give a 20deg drop @ 38kW)

i take mine out of the box, remove the annoying red cap and chuck it in the scrap bag... :30:

 

[lame plumber]

this was discussed a while back on another thread and explained in detail so just do a seach on autobypass to find it and all will be revealed,if not just turn off all your trvs and open the bypass until it flows and your there in simple terms.

 

[doitmyself]

I did fit a auto bypass the last time but never set it up properly. Can anyone tell me what setting it should be on ?? It is a Vaillant 438 with a grumfos 25/55 pump.

Is the system balanced for an 11C or 20C differential?

What setting is the pump on?

Which make/ model ABV ?

 

[eagleeye]

balanced for 20c
grumfos 25/55 - setting on 3
honeywell - DU144 (maybe need to change this for a DU145 ??)
Vaillant 438

 

[southcoastboile]

Rightly or wrongly I just hold my hand on the pipe and open the bypass really slowly untill I feel the heat start to come through then leave

 

[SafeGasInstall]

Call for heat and run on he and ch ,
then turn room stat down and cylinder stat down
keep programmer calling for heat on he and ch
then slowly start undoing it until it starts flowing through type valve
then turn up room stat and run ch and make sure it does not go through by pass
then do the same for hw
If all good then turn off and do test again just to make sure is all ok
then SCREW on the red cup and have a cup of tee

 

[SafeGasInstall]

And last make sure you know how to wire system correctly !!!!

 

[doitmyself]

balanced for 20c
grumfos 25/55 - setting on 3
honeywell - DU144 (maybe need to change this for a DU145 ??)
Vaillant 438

Those figures raise many questions about the actual installation, but that's another topic! Assuming they are correct, the DU144/145 will need to be set between 4 and 5.

 

[lame plumber]

Call for heat and run on he and ch ,
then turn room stat down and cylinder stat down
keep programmer calling for heat on he and ch
then slowly start undoing it until it starts flowing through type valve
then turn up room stat and run ch and make sure it does not go through by pass
then do the same for hw
If all good then turn off and do test again just to make sure is all ok
then SCREW on the red cup and have a cup of tee

surely if you turn down your rm stat and cyl stat youll turn off the pump and boiler?

 

[SafeGasInstall]

No as if wired ok pump over run would be still runnig mate for about few minutes and this is when you actually there is a need for the auto by pass to get rid of the heated water from heat exchanger and to save the pump