S53 Code on Vaillant ECOTec plus 428- 28KW Boiler

[Agile]

The problem here is LOW Return temperature, not runaway Flow temperature. At the various flow rates involved, the contribution of the bypass to the temperature of the Return is minimal.

You may think of a bypass doing that because thats why they are usually installed.

However, your problem is a too low return temperature. Lets not call it a bypass if that bothers you. Just call it a return temperature enhancer or anything else.

The function is to present the boiler with what it expects, a return which quickly heats up as it would find in a typical10 rad house and so enables the flow temperature to rise quickly to what the system expects to see.

[ Actually all that needs to be done for heating is to set the nearest rad to take more flow than it should. No new pipework needed ]

Tony

 

[kevplumb]

Just suppose, that in a fairytale world...................

of rabbits and hares.......................

there was a magic valve that bypassed about 20% of the boiler flow back to the return..........

then that might raise the return temp to prevent the boiler stopping on a Δ 16°..........................

perhaps the flow temperature might then rise to 72° and perhaps magically by then the return from the system might have reached 56° and the boiler might continue to operate like that if the magic bypass was closed ????????????????????

All these magic things may be possible in wonderland............

just suppose in a fairytale world you where sober

 

[croydoncorgi]

Tony
Back in the real world including carpets, tiled floors, furniture, etc. it's difficult or impossible to even work out which is the radiator 'nearest' to the main Return!

And anyway, I DID actually try to force the Return temperature up by wedging the DHW zone valve open, so that there was a short loop through the cylinder coil. Couldn't get enough through it to make much difference to the combined Return temperature at the boiler.

 

[Agile]

John, how does it respond when its cold started with a demand for CH and HW?

Is the HW flow balanced to a particular differential?

Tonmy

 

[adamneve]

HI

Seems to me that S53 is a design flaw

My system
5bed house 18 rads
438 ecotec open vented
15/60 pump
3 x single port valves zoned to cylinder/upstairs/downstairs
2 room stats upstairs and downstairs
Cylinder stat
Bypass valve at 4 bar
22mm pipe downstairs
28mm pipe to cylinder
15mm pipes to upstairs
Magnaclean
All pipework flushed
All rads removed and flushed

Having read rthrough the forum regarding s53 fault there seems to be no definitive solution?

My point is this that if i run the system with all ports open then i can run it at 30kw
if i only have the hot water cylinder open as in summer time then i have to manually adjust the rating down to 15kw or it will spend hours at the s53.

surely this is a boiler design fault?

 

[Agile]

HI

Seems to me that S53 is a design flaw

My system

Bypass valve at 4 bar

Having read rthrough the forum regarding s53 fault there seems to be no definitive solution?

My point is this that if i run the system with all ports open then i can run it at 30kw

if i only have the hot water cylinder open as in summer time then i have to manually adjust the rating down to 15kw or it will spend hours at the s53.

surely this is a boiler design fault?

A bypass set at 4 Bar will have no effect on the system at all!

If it was set correctly then it might make the system work better!

Even so I think your boiler is probably well over rated. What is the whole house heat loss?

Tony

 

[scw24489]

S53 means insufficient flow through the boiler - the reasons for this can be many.
Amongst the many potential reasons the OP mentions 22mm pipe on a 28kW boiler?!?
If the flow through the boiler is sufficient the flow temperature will not rise uncontrollably, your preference for hydraulic layout to achieve this may vary.
Systems of this size cannot be cobbled onto old rad systems without knowing significant details of pipe layout and sizing, they must be designed, you cannot expect to get away with hooking boxes together.
Good practise is a given!

Simon

 

[adamneve]

Thanks for the replies
The boiler is an ecotec 38kw boiler
All pipework is in accordance with the installation manual
The pipework to the cylinder is 28mm down to 22mm at the motorized valve.
The cylinder is 6 metres away from the boiler with a head of 1 metre.
My point is this that in theory this boiler should be able to run at full capacity on the cylinder only ? is this correct?

The bypass valve was set at the time of installation by the installer.
Maybe this is the problem Tony , whats the correct setting?

Steve

 

[mickyg]

the pumps too small and the boilers too big. As always with S53 problems the system is at fault and the boiler gets the blame for highlighting it

 

[adamneve]

Mickyg
Pump has been uprated to a 15/60 so whats the next step in pump size?


Tony the whole heat loss is 20kw plus the DHW at around 5kw
I know the boiler is well over rated but i am planning a major extension later so i bought this with that in mind.



Steve

 

[mickyg]

has the boiler been range rated? range rate it to 20kw using D0 that willl probably sort the problem.
a 438 would prob need a 25/80 pump

 

[scw24489]

Steve

The d0 parameter range rates the central heating mode only so depends what control setup you have as to how effective it will be.

From you don't say what sort of/size cylinder you are using but inferring a 22mm coil and an unvented cylinder the DHW coil is likely to be nominally rated at less than half that of your boiler, quite possibly less!

If you are having a 'major extension' it would probably be a good time to revisit the overall system design/sizing/piping techniques and controls

Your boiler requires a flow through the heat exchanger of 1600l/h with a dT of 20deg - at this flowrate it has an equivalent resistance of 4m water gauge. A 15/60 pump into 4m head will shift 1300 l/h at max setting so even if you connected the pump directly across the flow and return of the boilerthat pump isn't up to the job, add in the system resistance and you haven't got a hope!

Given that your existing house has losses of 20kW at max design point and any extension should likely be constructed to a higher energy efficiency spec then you are going to be more than doubling the size of the place to warrant that boiler!

Simon

 

[adamneve]

thanks
scw and Mickey
I am at the moment running the boiler d0 at 19.
So at that rate does that mean the flow rate required is halved?

When temperatures drop i increase it to 25-30

You would think that the electronics would automate this process?

 

[mickyg]

it doesnt quite work like that. But the lower the kw output the lower the flow you can get away with. So yeh at 19kw your 15/60 will be fine.

 

[Agile]

Tony the whole heat loss is 20kw plus the DHW at around 5kw
I know the boiler is well over rated but i am planning a major extension later so i bought this with that in mind.


Steve

The guidance for boiler sizing requires an allowance of 2 kW for water heating! Why have you exceeded that?

The rads are totally unable to exceed their heat output. In practice most hardly give 80%.

Whatever you reply your boiler is seriously overated by nearly 100%.

Whilst that gives flow problems it also gives problems with excessive cycling due to its too high minimum heat output. Did you not consider this when choosing the boiler>

Is this your own choice or did you take any advice from any professional? ( Although many professionals also suffer from a compete inability to understand boiler sizing in spite of having been on the appropriate course in many cases! )

Tony