Vaillant 438 with 3 zones, frequent S53

[matt1e]

Because Ignoring the valve of d0 or not has no impact on why it is shutting down with a S53 error
It's doing it to protect the heat exchanger from thermal shock

Matt

Could you elaborate ? Why does the boiler need to protect itself from thermal shock at d0=26KW, but not at d0=18KW, if d0 is ignored ?

Because at d0 = 18 the output is not as high and so the boiler delta t isn't either
It doesn't matter if d0 is ignored, it still monitors flow and return temps
S53 = too high delta T simple as that
Just a thought though When you say it ignores the d0 setting do you mean it always fires at the same rate regardless of the d0 setting?
Then that I can't get my head round either

Matt

 

[scoobydo123]

Yes the boiler fires at a percentage of maximum output of the boiler. I have not perceived any difference in the first 50 seconds on 428's whether d.0 is set to 30 or 5, perhaps it is different for the 438 series? Can the OP check the fan speed during the first 50 seconds when set to 18 as opposed to 38.

@ Alec

The one you went to yesterday how comes that has the software? Was this via request or fitted during servicing/fault finding by Vaillant?

 

[matt1e]

why would it protect the heat exchanger from thermal shock, yesterday I was in front of a 438 on a header (and new PCB). After heating the hot water cylinder at 80c, it went straight over to heating, and the flow temperature dropped within two minutes from 80c to 30c...before the boiler fired up.

As one would expect the primary pump stayed on, the cylinder pump shut down and the heating pump came on...

the boiler flow temp settled at about 30c for a while before it sought its compensated temp of about 45c....and it Hung in at 45c, for a good while...40 minutes or more..

I'm confused by this post Alec as what you are describing seems perfectly normal to me.
If you mean the fact that the boiler went from 80 to 30 within 2 minutes then that would not necessarily cause thermal stress as the return temp would have tracked the flow and been within delta t limits, it's the temperature difference between flow and return that can cause problems if too great,
I'm just guessing here, you will know these boilers far better than me as I'm more from a commercial background
Thinking about it when I say s53 is derived from a too large delta T and the boiler is protecting itself from thermal stress I'm probably wrong it's probably more of a dry firing protection as thermal stress is caused more by a sudden drop in return temp due to a large zone suddenly opening from cold for example, normally a bypass would protect against this.

My apologies if I am just adding to the confusion

Matt

 

[picasso]

A vaillant trainer told me s53 is to stop linear expansion of the heat exchanger. they dont want the front of the heatex to be 75 and the back to be 20, sounded a reasonable explanation (to me anyway).

 

[matt1e]

A vaillant trainer told me s53 is to stop linear expansion of the heat exchanger. they dont want the front of the heatex to be 75 and the back to be 20, sounded a reasonable explanation (to me anyway).

this is what I was getting at Picasso

Matt

 

[ALEC1]

Matt you are not adding to the confusion, its an interesting point about the bypass, but you wouldn't put one with a header...

my point was that a drop in temp from 80 to 30 in two minutes must be a pretty big thermal shock that was/is tolerated by the heat exchanger

 

[matt1e]

Matt you are not adding to the confusion, its an interesting point about the bypass, but you wouldn't put one with a header...

my point was that a drop in temp from 80 to 30 in two minutes must be a pretty big thermal shock that was/is tolerated by the heat exchanger

no its not the same sort of thermal stress as in your example the burner is off and the HEX is being cooled by the lower temp entering the return this is bringing the temperature of the hex down uniformly as in your example the flowrate is suited to the boiler, and if you had monitored the return temp then you would have seen that it wouldn't have been much lower than the flow temp
problems arise when there is too much difference ie the burner is firing, one end of the hex is up in the 70s and the other is below the 30s for example

The trouble with the ops system is the size of the zones while the heat is going around the system, at the boiler the flow is getting hotter but the return is lagging, the newer software may result in a slower ramp up time, it may look at the return and decide how much burner power to apply, I don't know but one thing is for sure the ops problem as it stands now is down to the flow-rate through the boiler
It probably would have been better to install it as a Primary/secondary system
The op would probably benefit from a correctly sized modulating pump
other than that its going to require bypass's or better burner control (presuming that 0-10v is an option)

Ps you do actually get system/boiler bypass's installed on primary loops too but we're talking larger systems here

Matt

 

[ALEC1]

By passes on older system primaries were to avoid condensation...I can't see any reason to put them on a condensing boiler primaries..

 

[Bunnyman]

Sorry to join this thread so late but please be tolerant of Alec he posts in here an this is his pet thread, he is WRONG so many times ... The s53 is caused by systems not being fitted correctly or pump sizing wrong .. MANY people have told Alec that the pcb has been changed because it makes the vaillant more tolerant of POOR installation pipe sizing or design (but it's like banging your head against a brick wall!) not because of an inherent fault he seems to rant about. He seems to suffer more than most because of inexperience ! Sorry rant over

 

[ALEC1]

lol BM....so why did not senior product managers and technical people from vaillant point out my errors in the installs...its not as if they have not seen them.

It is true I have very little experience of problem installs though, on that I do agree!

 

[ALEC1]

and the problem with vaillants own compensation controls on their own 400 boilers was Microfiring not s53s...

 

[Bunnyman]

They were not senior managers as you are well aware, I have spoken to people an know you were told many times until people eventually gave up hence why the powers that be will have seen this thread an disregarded it , I'm sorry for the op , as they won't get the advice they need an I do wish you would stop posting on the subject it's very frustrating

 

[ALEC1]

BM you are outrageous.

That vaillant changed software speaks volumes....nuff said!

and yes lots of people here gave advice, but it was not the same as Vaillants.

Note this was to resolve micro firing issues with compensation controls, not repeated s 53's on on off cotrols!

Updating the PCB seems to have cured both, and that (obviously) does not mean that the wrong sized pump can be used.

 

[Bunnyman]

 

[Onetap]

By passes on older system primaries were to avoid condensation...I can't see any reason to put them on a condensing boiler primaries..

I thought their main function was to maintain a minimum flow rate through the boiler. A by-pass may be useful on a system with TRVs fitted on most radiators, but the Building Regs (ISTR) require them to be ABVs, rather than fixed by-pass valves.