Vaillant ecotec plus cycling on HW only demand

[Agile]

Whilst someone like me might do this its only mentioned for amusement!

The problem is the 50 secs of firing at 75% which increases the return temp and that turns off the boiler for a variable time but not as long as the set anti cycle period !

The flow to the HW could be 'stored' in a well insulated buffer store of about 10 - 15 li connected in series with the HW coil!

Tony

 

[scoobydo123]

Is this thermal buffer just a radiator in a well insulated box or can they be purchased off the shelf. Just on my way there to draw of 30l and see if it can cope with some cold water to dump heat into

 

[Agile]

I am not aware of any off the shelf component for this application.

If I was doing this then I would modify a duff expansion vessel.

It was only suggested as a technical solution! The correct solution would be to modify the pcb software.

Another possibility would be to use a pcb designed for a 600 series system boiler.

Tony

 

[scoobydo123]

Right done some testing. on initial fire up.With cylinder satisfied and me turning it up 5 deg the boiler fired and managed to pass the 50 second threshold ie went into modulation mode. I then drew off 30L of water and then switched HW on. The boiler then fired for the below sequences elapsed times

6min 54sec
on 10:07 off 10:10
on13:02 off 13:15
on 16:01 off 16:16
on 19:00 off 19:11
on 22:03 off 22:10
on 24:54 off 25:04
etc etc.

Very interested if you are able to modify the PCB or if a 6x will fit maybe you could send me a PM with costs etc.

Thanks for your attention

Other option is could I take a feed of the firing circuit which I will then feed into a time relay to open the CH circuit for 45 seconds and then close thus giving the boiler a chance to reach the modulation stage.

 

[UpgradeME]

The boiler then fired for the below sequences elapsed times

6min 54sec
on 10:07 off 10:10
on13:02 off 13:15
on 16:01 off 16:16
on 19:00 off 19:11
on 22:03 off 22:10
on 24:54 off 25:04
etc etc.

Are they MM:SS? i.e. The boiler fired for 10min 7seconds (ON) then switched OFF for 10mins 10seconds (for the first line)? or something else???

What does the 6min 54sec refer to?

 

[Agile]

Those results dont show the 50 secs as causing any problem.

All I can suggest is that you reduce the anti cycle to the minimum but unlike other makes its not the only aspect which determines the waiting delay before refiring. Some of the others may have suggestions for other parameters which might be advantageously be changed.

No one I know of can change the software in the 400 pcbs. Nor do I know what may be involved in trying to fit a 600 pcb to a 400.

Tony

 

[scoobydo123]

Ok done it quickly before taking my lad football training. So from warm boiler primary around 40 degrees. On the first call for heat the boiler ran for 6 min 54 sec before shutting down it then fired again @10min 7 seconds until elapsed time of 10min 10 seconds (i.e only on for 3 seconds). The boiler then fired again at 13min 2 seconds after the initial call for heat so just under 3 minutes elapsed after the previous call for heat etc etc.

Tks

 

[scoobydo123]

Tony the boiler is only firing for around 6 seconds per cycle. Only on the initial fire can it dump enough heat to actually go to the modulation mode after this has happened once it then goes into 6 second mode. So first fire it lasted 6 min 54 after which it fired again after 3 minutes for just 3 seconds.

 

[UpgradeME]

Tony the boiler is only firing for around 6 seconds per cycle. Only on the initial fire can it dump enough heat to actually go to the modulation mode after this has happened once it then goes into 6 second mode. So first fire it lasted 6 min 54 after which it fired again after 3 minutes for just 3 seconds.

So the above restated as (MM:SS):

WAIT --- BURN
00:00 --- 06:54
03:13 --- 00:03
02:52 --- 00:13
02:46 --- 00:15
02:44 --- 00:11
02:52 --- 00:07
02:44 --- 00:10

During the WAIT times, did you notice what it displayed on the LCD? (S.7, S.8 or S.53?)

You mentioned you have D.0 set to 11. Have you changed any of the other settings away from their defaults? Did you check what D.40 and D.41 were doing during the initial phase / then cycling?

I'm guessing there was a bigger delta T during the initial 6min burn phase, the delta T then lowered as it reached the set temp.. The subsequent burn phases then generated too much heat during the first few seconds to be dissipated by your coil, resulting in the boiler cycling.

 

[scoobydo123]

Yes correct on the times, not sure what is displayed during the waits as I was monitoring D40, D41. D40 quickly rises to 70 target flow rate with D41 rising very quickly as well had to monitor between different cycles due to it only being on for a very quick period. D40 has dropped to 61 when it fires back up anti cycle has been set to 5,pump over run 11 and D0 11 everything else at default.

 

[UpgradeME]

Did you make a note of the D.41 values? I'm particulary interested in the delta T (i.e. the difference between D.40 and D.41) on the initial burn phase and what it was at the point it switched off at 6min 54 seconds in to better understand what the boiler was doing?

This information will also enable the calculation of flow rate through the boiler.

Did you check what the ABV or pump was set at during your visit?

 

[scoobydo123]

Hi again,

I think it was at 61 when it switched off (boiler set to 70) however I will run another test. Pump is set to speed 3 (it is a british gas/ scottish gas rebadge of grundfos) ABV was pointing at the digit 2.

Also did look at the d parameter that is for flow per min and this was displaying 0

Thanks

 

[UpgradeME]

I think it was at 61 when it switched off (boiler set to 70) however I will run another test. Pump is set to speed 3 (it is a british gas/ scottish gas rebadge of grundfos) ABV was pointing at the digit 2.

When checking again, if you can provide a few examples of d.40/d.41 during initial phase, at turn off & then during cycling? Please also note the S.xx code displayed after it has switched off which may be useful!?

It might also be worth trying return sensor regulation (change d.17 to 1) which sometimes helps!

Also did look at the d parameter that is for flow per min and this was displaying 0

It would appear that the same firmware (PCB software) has been used across a number of Vaillant boilers as there are many d. codes still present on the 4xx boilers that are redundant.. d.36 is one such code as there is no HW flow sensor on the 4xx boilers!

 

[scoobydo123]

Ok will do, I did see the D17 parameter, with this set away from default should I change target temp to a different value from the current setting of 70? Otherwise I would imagine that flow will end up being very close to overheat. When I read the manual it seemed to interact with the target temp. Think I am going to struggle to get this to extend the burn time by around 400% to get into the modulation zone. Have spoken to Valliant tech support who are not aware of the 50 second timer and suggested I have a sludged system.

 

[Agile]

Dont expect Vaillant tech help to know much detail about their boilers. They can read the manual back to you though!

OP, you seem to be trying to heat an already hot cylinder!

If you start with a cold cylinder then I would expect you would get a good long burn.

Tony