Vaillant anti-cycle time question

[fezster]

A quick question for anyone who's familiar with Vaillants.

Boiler is an Ecotec Plus 438 and I wanted to know if the d.2 parameter applies to S53, as it does to anti-cycling?

From the manual:
d.2
Max. burner anti cycling period at 20 °C Flow temperature

Thanks!

 

[scoobydo123]

not sure what the question is but here is what d.2 is

 

[fezster]

View attachment 131784 not sure what the question is but here is what d.2 is

Thanks, I'd found this pic already, and I've set d.2 accordingly.

However, I don't think it does apply to S.53. In fact, S.53 seems to have a mind of it's own. Sometimes it'll recover after a few mins, and other times I've waited for over half an hour and it's still showing (not walked away, so it's not come out and gone back to S.53).

 

[scoobydo123]

S.53 will be satisfied as soon as the logic is happy with the Δ between flow and return I believe.

 

[fezster]

I monitored d.40 and d.41 whilst the boiler was in S53. The delta was always less than 10. I haven't established if there's a pattern between the delta and the boiler coming out of S.53. Shockingly, none of this seems to be documented in the Vaillant manual!

 

[scoobydo123]

What are the actual D.40 and D.41 values? Is the S.53 after cold start? How old is the PCB?

 

[fezster]

D40 and D41 will vary, but always with a 20 degree delta when the boiler is firing normally. I posted this on another forum but I'll quote here to give some context:

I have an upstairs zone, donwstairs zone, HW zone. Only radiators, no UFH.

I've monitored D40 and D41 for individual zones and zones in combination. The delta is always roughly 20 degrees now (I say now, because it took some fine tuning to achieve). It may creep up to 22 degrees, but no more.

It's *only* when a cold zone (say upstairs heating) opens whilst another zone (downstairs heating) is fully hot. So D40 will be 70, D41 at 50 - then the upstairs zone opens and D41 shoots down to 30. Boiler sees the large differential and goes into S53. It then waits an arbitrary time (must be some logic to it?) before powering to full power again. At which point, the delta is again 20.

However, what happens far too often is that whilst in S53, the u/s room stat becomes satisfied and closes the zone. When the boiler comes out of S53, it's only the d/s zone open and so it fires back up to 70/50. Then the u/s zone opens again and the cycle repeats. I should note this sequence doesn't happen all the time, but far too often. The result is that the d/s zone always remains luke warm and the stat temp is never satisfied. This may be because during the day (on weekends) we have the d/s quite hot with young children in the house, and leave u/s relatively cool.

So when the boiler hits S53, D41 is around 30 (because of the cold water from the other zone being mixed in), and D40 comes down from 70 odd to about 40 (i.e. the boiler modulates right down to protect itself). It'll then stay at that for an arbitrary length of time whilst D41 creeps up. Not sure what the relationship is between D40 and D41 for the boiler to come out of S53.

I also suspect (not proven) that the boiler increases the S53 duration every time it occurs, exacerbating the situation.

 

[scoobydo123]

Unfortunately the logic on this boiler is a hodge potch affair. I would say most systems would have the same behaviour when DHW has called for heat and then CH calls so does appear on the face of it that something is amiss. I havent seen the problem. What is d.0 set to I think there is some undocumented realtionship between d.0 and other paramenters. Maybe a new PCB with the "enhanced" logic will get round the issue. I have also seen the boiler not follow the logic of d.2 on occasion.

 

[fezster]

I have the enhanced PCB as of 4 years ago. There was a previous long thread on here where someone told me about it (was it you?) and I asked Vaillant to install it for me (which they did).

I would say most systems would have the same behaviour when DHW has called for heat and then CH calls so does appear on the face of it that something is amiss.

Completely agree. Although in that instance, the S53 usually occurs just the once (as the cylinder will heat up and then stat will turn off - even if it calls for heat again, the water temp will be higher in that zone, and the problem occurs when a cold zone flushes the return with water). With 2 heating zones - and in particular when one zone thermostat is significantly lower than the other - the problem is much more likely to occur, as Im experiencing.

I'm confident the answer is a Low Loss Header. It'd be nice if a commercial guy on here could confirm that. I do have an engineer coming next week to quote me, so will obviously ask him to confirm the same.

Thanks for your input scooby.

 

[scoobydo123]

I get no S.53's under any scenarios. Yes it was around 4 to 5 years ago that I done all the research into the odd logic of the boiler and do remember your thread. I think a few heating engineers finally agreed on the logic issues around this boiler. I have read someone else saying that there is a new PCB that ramps up slow but not sure if that is the case or just anecdotal hear-say. The gloworm sxi has the same HEx iirc and that starts low and works it's way up. That also has a bit of an issue where it waits 5 or so mins even when the return temp is dropping when zones open, didnt get anywhere with product support for that boiler though. Unfortuntately the whole multizone issue is something that in the UK was never popular and the logic on this boiler was always a bit kranky. Hopefully as more and more we push for efficiency then it will become more popular.

Before getting the LL maybe get hold of vaillant and see if there is indeed a "revised" revised PCB available. Have you tried lowering your flow temp. Do you have an unvented cylinder as you can store the water a bit colder so you can still satisfy the cylinder on the first burn. You may uncover a sweetspot on the logic that gets rid of your issue. Or maybe set it up for return sensing rather than flow. Bit of poke and hope I am afraid but maybe one of the others on here will be able to help.

 

[fezster]

I've lived with it for 5 years, so it's not the end of the world. But I've decided I'm going to get it sorted now so hopefully the LLH will be the right solution.

The boilers also out of warranty, so not sure vaillant will be interested. I plan on calling them on Monday to see if they can offer any useful advice.

What did you mean by set it up for "return sensing"?

 

[fezster]

Ah, just found this:

http://vaillantcyclingproblem.blogspot.co.uk/2011/12/return-sensing.html?m=1

Will have a read.

 

[scoobydo123]

return sensing is took from the NTC's so it will operate the boiler based on the sensor that reads the value for d.41 rather than d.40 it is just a binary setting in the normal service menu IIRC.

 

[fezster]

Just had a play with the d17 parameter. Not exactly sure how its supposed to work, but when heating just my cylinder at 75 degrees, the boiler cycles once the return temp (d41) hits 50 (flow temp 65). Did this 3 times until I stopped it. I'd imagine it'd take quite some whole to heat the cylinder to 60 degrees at that rate.

With d17 as 0, the boiler would modulate down rather than cycle, allowing the cylinder to heat in a single cycle. So unfortunately this setting is a non starter for me. Was worth a shot though!

 

[scoobydo123]

how did you get the boiler to call for heat? Hopefully not by cranking up the cylinder to an artifically high setting without actual draw off as the boiler will mis-behave if you try that Is it an unvented cylinder? What is your normal setting remember they have quite a wide range I find if unvented and you have a large enough cylinder then 50 c out at the taps is a good setting. You should then be able to reduce flow temp.