Vaillant ecotec plus cycling on HW only demand

[kevindgas]

is the boiler wired up via a standard wiring centre or a Vaillant VR61/65?

 

[scoobydo123]

Boiler on standard controls and wiring centre.
Tony if I draw off 30l of Hot water I only get one good fire it takes an age to get a full tank full

 

[kevindgas]

don't think I can help much then. if on a VR you can set hot water part load in D.77 to range rate to suit the cylinder coil
but I don't think it works with standard controls but still worth a try I usually set it to 12Kw (factory set at 30Kw)

 

[MrV]

Looks like you're dealing with a flow or transfer issue as has already been suggested by experienced engineers and overlooked or ignored. It seems you may think that somehow tweaking settings on the boiler of which you don't really understand or know what they are for and don't know the adverse affects you are creating by changing them, will fix the inadequacies.
I'd suggest getting an "Engineer" in that does know what he's doing and let him diagnose it correctly.
It's a GAS boiler after all and some settings you are "Playing" with, require second level access. There's a reason for that!
With the greatest respect, there is a level DIY that can be applied with regard to gas boilers and if it wasn't for the stringent safety features that have to be fitted to them, (the sort of stuff that people generally think is ok to "Tweak") it would probably be another flattened house the list.

 

[scoobydo123]

MrV, if the boiler didn't run at 75% of max output then it would be fine hence asking for advice here from guys who actually seem to have knowledge of boiler controls and have some passion about their job. I have spoken to 3 local gas safe engineers all of them unaware of the firmware behavior of the boiler and they did not fill me enough confidence that they would have the knowledge to fix. I would like to ask has anyone got a 428 that is on relatively short pipework(approx 4m away) to a megaflo got it working without these issues? Realistically could I have an issue with scale at the bottom of the megaflo? If I was getting a secondary burn of say 40 seconds then at least I would only need to find 10 seconds before modulation occurs but currently I need to find 40 seconds from somewhere.

I am not changing settings willy nilly and wouldn't without first understanding how it interacts.

Kevindgas wouldn't mind updating controls if the boiler does respond to the setting of D.77 for the full duration of the burn rather than wait for 50 seconds before looking at this parameter as I am sure it will be ok.

Tks

 

[The831Bunny]

Your first port of call as I and many have said, is to check and PROVE that the boiler is getting the correct minimum flowrate of 20 l/min through it while heating the cylinder. Did you check the pump? Is there a resistance on the primary circuit? Fault finding has to be based on fact and elimination. This coupled with engineering knowledge and experience will lead to a successful diagnosis and repair.

The Megaflo coil could be scaled. You would know if your water was particulary hard by shower heads/kettles etc. If it was an early 145, then the coil was vertical (not horizontal like the newer versions) and there is quite a gap at the bottom of the cylinder for a bucket full of scale before it really affects the whole coil. 'Usually' thick scale breaks off the coil with it flexing, but my money is still on it being low down the list of possibilities.

Mr.V, by the way, draws on a huge knowledge of all that is Vaillant. He is rarely ever wrong

 

[scoobydo123]

Circulation seems ok if CH only is selected so can only assume that the HEX is ok and that there could be a restriction in the primarys to the cylinder however flow and RETURN seem to get hot very quickly albeit obviously not maintaing the required . How can I check and prove that the boiler is getting the 20l/min required? Yes it is a hard water area. I will pay another visit and check to see if the pump can be stopped with a screwdriver, did bleed the pump when last there and there was no air and only a small weep of water came out.

Not questioning MrV knowledge and only glad that he has took an interest. Perhaps he could confirm if I do change to valliant controls if it will react to D.77 immediately. Also perhaps he could confim what rev of PCB does not contain the intial fire at 75% of max rating so I can try and source one.

Thanks

 

[UpgradeME]

How can I check and prove that the boiler is getting the 20l/min required?

See my earlier post (below) as you have not yet provided the info:-

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.

With the Vaillant controls fitted you can have different max kW values for CH (d.0) and HW (d.77). However, this will not make any difference in your situation as you have effectively down rated the HW via d.0 to 11kW already.

 

[scoobydo123]

Ok will get the info requested and also try to get gas usage from the meter during these measurements if useful.

 

[scoobydo123]

Right got my partner to go round there and get the figures however she had problems getting the S codes so can get them later if required.

So British/Scottish gas grundfos pump
D0 set to 11kw
Flow temp target 75
No call for heat and D40 43 D41 44
Turned stat up on megaflo so call for heat (cylinder already satisfied)
The following figures apply for d41 at the timings given
Temp,Minutes/seconds
45,0:30
61,1:00
58,1:04
59,1:09
60,1:13
59,1:24
60,1:28
61,1:30
62,1:33
63,1:34
64,1:35
66,1:39
67,1:44
66,1:45
65,1:52
66,2:08
67,2:12
68,2:24
69,2:27
70,2:30
71,3:04
71,3:26
72,3:58
72,5:03 (boiler off)
71,6:00 (cooling stage)
70,6:34

Couldn't get her to get the gas reading unfortunatley at the same time.

I could hear the boiler go quieter at 50 seconds when it takes onboard the 11kw setting and you can see from the measurements that the boiler had reduced output at this point

 

[UpgradeME]

In order to calculate the flow rate, as previously mentioned we need the delta T which is the difference between flow and return temperature (you have only provided return temp).

Do you know what d.40 was at any points above? (especially at the beginning and at around 3-4 minutes )

If it was 75C at 3-4 minutes (as you would expect), then the flow rate would have been 20 l/min so okay (5.6/4.2*60/4=20) - Do you have any d.40/d.41 figures for when the boiler is cycling?

I could hear the boiler go quieter at 50 seconds when it takes onboard the 11kw setting and you can see from the measurements that the boiler had reduced output at this point

On my 418, the kW for the initial xx seconds is a percentage of d.0 NOT a percentage of the highest setting (28kW in your case). To verify yours, empty some hot water then change d.0 to 6 and listen to the sound it makes for the first 50 seconds, then change d.0 to 28 and listen again.

If the burner/fan sound the same, then your boiler is as you say a percentage of 28kW (75% for the first 50 seconds will be 21kW). If it's a lot quieter when d.0 is set to 6 then it's 75% of d.0 (11) so 8.2kW for the first 50 seconds.

 

[The831Bunny]

UpgradeME: checked a 2007 418 yesterday and it was doing (D.33) 258 for initial 45-50 secs, then rising to 410 (18kw). I took that to be 63% actually I'm not sure where I got 75% from. Maybe have a look at yours and see if there's any difference with BMU releases possibly. D.0 setting made no difference.

Scoobydo: It looks from your D.41 results the cylinder was already at 60C when you started your test . It really needs to be cold or at least below 40C for a reliable delta T. The boiler may well have begun to modulate towards the end of your test.

 

[UpgradeME]

UpgradeME: checked a 2007 418 yesterday and it was doing (D.33) 258 for initial 45-50 secs, then rising to 410 (18kw). I took that to be 63% actually I'm not sure where I got 75% from. Maybe have a look at yours and see if there's any difference with BMU releases possibly. D.0 setting made no difference..

Thanks for the info! I'll do some tests tomorrow and also see if I can identify which system board is installed in my boiler (it's circa 2010/11, do you know what was installed in the above?) as this seems to come up often - ISTR from my tests last year it only lasted for 20 seconds (not 50) and d.0 made a difference with mine (and others on DIYnot have said the same). I have a VRT392/VR65 installed but can't see that making any difference to this operation!?

EDIT: Okay, I was curious so just carried out the following two tests:

Test #1 - Increased room stat to demand 25C (room was 20.5C with boiler off)
d.33 started at 258 for approx 2-3 seconds then increased to 276 and stayed there for over a minute (I then turned back the room stat so turned off the boiler)

Test #2 - Turn on HW demand - cylinder at 47C and demand at 55C
d.33 went to 209 almost immediately (could have started at 258 for a couple of seconds max) and stayed there for over a minute.

d.77 is set at 8
d.0 is set at 10

I'll check the system board number/revision tomorrow.

 

[kevindgas]

the 428 with a megaflo cylinder seems to run ok since group service lad adjusting D.77 no issue that i'm aware of. 392 room stat and vr65 system.

the other 418 with an oso solarcyl worked perfectly with d.77 adjusted whilst operated with a 392F and VR65 now its running on a 430F and VR61 set up (see my other thread) there are issues with the UFH side but no issues on the water side that i'm aware of

still a few issue with that one that hopefully i will sort tomorrow!

 

[scoobydo123]

Ok will try to get the extra info today it is just quite difficult as I dont live there. Just wish my one behaved like upgradeME where it takes the percentage value of D0 for the first x seconds. Will also see if it will let me set D77 without having the VR controls.

831 Bunny yes cylinder was at around 60 when test carried out not sure it is going to make much change to the issue if I had 145L of cold water after the initial burn. On my earlier test after drawing off 30L of hot water it resulted in a longer first initial burn as expected but still nowhere near enough heat transfer was taking place to reach 50 seconds of burn with 21kw of energy going into it.

Thanks