Vaillant 438 with 3 zones, frequent S53

[hazetimesfive]

Does parallel really give you the same head? Can anyone show me how this works mathematically

 

[matt1e]

Does parallel really give you the same head? Can anyone show me how this works mathematically

do a google mate plenty of stuff out there to chew on
quick explanation for starters
http://www.engineeringtoolbox.com/pumps-parallel-serial-d_636.html

Matt

 

[Onetap]

Does parallel really give you the same head? Can anyone show me how this works mathematically

Double the flow at the same head on the pump curve, i.e., in theory.

The actual flow, for any one pipework system, is the point of intersection of the pump curve and the system curve, so in reality you get neither the same head nor the same flow.

 

[fezster]

do you get S53 when set to 26kw though?
I take it the pumps are in series?
that gives you more head same flow rate
in parallel will give you same head ,more flow rate

you need to have adequate head and flow-rate, just because you have two pumps it doesn't mean that you have the correct flow-rate andhead

your system is large for a domestic application it needs a better design spec
The boiler is shutting down because it is protecting itself from thermal shock
do you have a differential bypass fitted before the zone valves?


Matt

At 26KW, the d/s is fine (Total rads = 26KW). The u/s has S53 (total rads = 18KW).

Yes, I have an autobypass fitted before the zone valves. This doesnt kick in on a cold system (i.e. it's not always bypassing, though Tony suggested this could be a possible workaround for this problem).

 

[matt1e]

Yes, I have an autobypass fitted before the zone valves. This doesnt kick in on a cold system (i.e. it's not always bypassing, though Tony suggested this could be a possible workaround for this problem).

and I agree it could

adjust it so that it is shut when both zones are open and it is open (bypassing) when either zone shuts off

try setting your boiler output to what you req,then set the bypass so that when the upstairs zone is on its own the boiler temp differential is within spec and you no longer get an S53 error

you really need to have the correct pump spec'ed and installed though

Matt

 

[Agile]

You need to note the actual words that I use!

I mentioned that it would enable the return temperature to be increased faster but in the same breath I also said that it would limit the maximum power output.

I also referred some of these things as quirks of the boilers operating. Many of the latest boilers start running at lower output power, watch the return temperature for a minute or two and then decide to increase the power, carry on at the same power or reduce the power.

Nobody here really seems to know what this new/revised/optional PCB really does but we do know that it will control the boiler better, if its being fitted to current boilers or how to identify it visually. If I ran Vaillant then I would tell you but I don't and I expect those who do don't take much interest in us or Alec. They probably see him as a bit of an irritant!

Having said all this IF a 4xx boiler is correctly installed with a properly matched pump then they do apparently work well.

Tony

 

[Agile]

Even if you cannot work out a controller to alter the d0 dynamically as required then you could still create a simple relay based logic to actuate motor valves to provide bypasses when required to fool the boiler into thinking everything is normal.

In fact it could all be housed in a Tupperware box and have digital displays on the front!

Tony

 

[matt1e]

Even if you cannot work out a controller to alter the d0 dynamically as required then you could still create a simple relay based logic to actuate motor valves to provide bypasses when required to fool the boiler into thinking everything is normal.

In fact it could all be housed in a Tupperware box and have digital displays on the front!

Tony

or you could do it the normal way and just swap the two ports for three ports
Tupperware boxes, relays and digital displays indeed!

Matt

 

[scoobydo123]

What is getting me is how when the system is cold changing to 18kw stops the s.53 that comes after 20 seconds. As we know these boilers dont take into account during the first 50 seconds the value of d.0 and just fire at around 70% of max rating. Havent read the full thread but has it always been like this since install or have you inheriated the system.

 

[Agile]

It will have been the same since install and also since he inherited the system!

 

[fezster]

What is getting me is how when the system is cold changing to 18kw stops the s.53 that comes after 20 seconds. As we know these boilers dont take into account during the first 50 seconds the value of d.0 and just fire at around 70% of max rating. Havent read the full thread but has it always been like this since install or have you inheriated the system.

Regardless of everything thats been said about the first 50 seconds being at full pelt, i can assure you that at 18kw in d0,the boiler definitely maintains a lower flow temperature when firing up than at 26kw. No s53 since changing to 18kw.

 

[matt1e]

What is getting me is how when the system is cold changing to 18kw stops the s.53 that comes after 20 seconds. As we know these boilers dont take into account during the first 50 seconds the value of d.0 and just fire at around 70% of max rating. Havent read the full thread but has it always been like this since install or have you inheriated the system.

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

 

[ALEC1]

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..

 

[fezster]

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 ?

 

[ALEC1]

vaillant PCBs are similar mostly accross the board, but other vaillant models have a composite material as the outside of the heat exchanger with a fuse that blows if it gets too hot.

Those models do need some sort of protection, although I have no idea at what temperature the composite material fails.

The 400 series has a metal heat exchanger, so it probably doesn't need such protection. Indeed you can pressurise a 400 boiler with no dry fire protection (ie no flow or pressure sensor) with no issues.