Vaillant Issues

[scoobydo123]

gazdaz36 on relatively short primaries I have seen issue with the 4 series in the start up behaviour running at around 80% of max rating of the boiler. I am concerned with if I go for smart controls and the boiler requests a low target flow temperature that I may end up getting stuck in an endless loop of overshooting requested target flow as the flow will ramp up very quickly due to the boiler running at around 22kw for 50 seconds. Not sure how someone would manage on a 438 (30kw startup). I picked my boiler due to the very low (at the time) modulating range.

 

[ALEC1]

well have a look at this:

http://vaillantcyclingproblem.blogspot.co.uk/

about the 400 series...

an acceptable performance can be obtained with this boiler with vaillants ebus controls by setting the minimum flow temp on the 470 or 430 to around 43c....not sure to what extent it is related to the start up sequence..

ebus(and OT) controls give longer pump running times and lower flow temperatures so I guess a lot of the benefit I see is from these...heat ultimately destroys everything and running a condensing boiler at relatively low temperatures must prolong its life

 

[vince101]

scoobydo123...you were after some data.

Only setting I changed was D0 to 22. D2 is still preset value of 20.

Typical flow temps for D41/D40 as follows (haven't timed...)

HW / CH
52/37 Delta 15
65/50 Delta 15
68/52 Delta 16
71/62 Delta 19

HW only
66/49 Delta 17
74/54 Delta 19
75/57 Delta 18
75/60 Delta 15

Cheers!

 

[scoobydo123]

All good by the looks of it. The key as you have found is having the system able to satisfy the controls without any cycling. If you cycle you are in big trouble with this boiler. You may find that you can turn your flow temp down a bit as this will help keep in condensing mode longer. What have you set your tankstat to as you may be able to decrease this as well. Also with a lower flow temp if you do end up cycling the anti cycle timer is longer at lower target flow. Mine is set to 60 (d.2) which equates to around 7 minutes at my flow temp which should mean if I do cycle then I stand a chance of enough heat getting out to not get stuck in the short cycle loop.