Vaillant 937 dhw problem

[Notapro]

Hello,

Just had a Vaillant 937 storage combi and rads installed, all done very nicely. However, when I turn off a mains fed cold tap, the boiler starts up, at least I can hear the fan coming on.

I thought this might be related to a dead leg with air in it somewhere in the cold water pipework, but as I have now bled out any air from cold supply side, I am slightly puzzled.

I would appreciate any thoughts before I get the installer back.

Thanks for your help.

 

[DP]

Air is in what use to be the HOT water plumbing now redundant.

 

[gas4you]

Commonly called a dead leg. Most likely where the old cylinder used to be fitted.

 

[Deleted member 105431]

set d88 to 1.

 

[Notapro]

Thanks for your replies. Air in dead leg now unlikely so will try higher threshold on d88.

Thanks again.

 

[Tipper]

I'm interested in this change to d88.

What is the standard setting from Vaillant? I assume it's 0, ie, 1.5l and no delay? 1 would require 3.7l and then delay for 2s.

Being a 937 with its 'ninja turtle' back-pack is this 2s delay long enough? Wouldn't you expect a longer delay which would allow water to be taken from the back-pack first and the boiler firing up say 10-20 seconds later thus avoiding unnecessary firing when a hot tap was opened either in error or for a few seconds only? Doesn't the back-pack have some overriding settings over the combi wrt recharging the cylinders?

 

[Tipper]

Just to take this one step further I had a look at my 937 wanting to change d88 to give the longer delay before firing but find that the 937 does not use d88. It's not listed in the manual as an adjustable setting.

Therefore my ramblings above on the 937 are nearer the mark in that the 937 'backpack' takes over control of the DHW demand depending on the 'backpack's' needs and the DHW re-charging timings. There is no user defined adjustment of delay before firing.

Just thought I'd let all know this.

 

[Agile]

Its possible that there are engineer settings which some others may know.

Its always better for a DIYer to ask the pro first before assuming anything.

Tony

 

[Deleted member 105431]

Its possible that there are engineer settings which some others may know.

Its always better for a DIYer to ask the pro first before assuming anything.

Tony

set d97 to 17 first then d88 will be enabled.