Vaillant EcoTec 428 configuration issues for Hot Water Only

Contrary to what has been stated above, my understanding is that the boiler ignites at close to MAXIMUM power and only turns down to the set value of d0 after about a minute.

Via observation, that's the conclusion I had come to, I'm glad someone else believes that's the case. It's partly the cause of the problem we are having, I'm sure of it. Because the heat is not dispersed quickly enough into the cylinder, partly because of the short circuit and partly because of the in-efficient transfer in the cylinder, the boiler never manages to reach the modulating (less than full power) part of it's cycle.
 
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There are three Honeywell valve
In physical appearance it looks exactly like this one:

I don't know if there are several different models that look exactly the same, but if not, it's definitely that one.
That's the DU144.

You need to remove the rad cap, then unscrew the adjuster until the bottom of the adjuster is on the 0.1 line.

Note: The cap is internally fixed with sealing wax during assembly. Turn firmly to break the seal.

With the heating on and all radiator TRV's fully open (i.e when heating has just started up), the valve should be closed, so the pipe on the side away from the pump should be cold. If it's not, close the ABV slightly until it is. As the TRVs close down the ABV should open - pipe gets warm. When the system is on HW only the valve should be fully open.
 
With the heating on and all radiator TRV's fully open (i.e when heating has just started up), the valve should be closed, so the pipe on the side away from the pump should be cold. If it's not, close the ABV slightly until it is. As the TRVs close down the ABV should open - pipe gets warm. When the system is on HW only the valve should be fully open.

More great info, the installer came back yesterday to upgrade the programmer from 1 day to 7 day, he also adjusted the pressure relief valve, the balancing valve on the hot water circuit (increased the resistance) and the anti-cycle timer. Since all are changed, System appears to be behaving better. I'll reserve final comment for a few days so I can keep a closer eye on how things are running.

There's still a degree of cycling (but intutition tells me a certain degree of that as target cylinder temperature gets close is unavoidable), but during the cycles a higher proportion of the water in the circuit appears to be heated (the boiler fires for longer), hence by the time the timer 'ticks' and the boiler re-fires, the flow temp hasn't dropped to much below the cylinder terget temp, so there is always heat transfer in the right direction.
 
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What temperature is the boiler flow set to when heating the hot water?

I would usually suggest about 72° but of course this has an effect on the heating. Its a compromise between boiler efficiency and reheat time.

Tony
 
What temperature is the boiler flow set to when heating the hot water?

I would usually suggest about 72° but of course this has an effect on the heating. Its a compromise between boiler efficiency and reheat time.

Tony

Flow temp set at 70. I can live with that, as the weather gets colder and we're running the heating at the same time as hot water, I can knock it down a bit and recharge times shouldn't be effected too much as there's less cycling when there's a higher circuit heat loss (ie via the rads).
 
It sounds to me as if the boiler is grossly over rated. What is the heat loss calc for your house?

Is this an old cylinder which cannot absorb even the minimum boiler output when its half warm.

It should fire at the max d0 power setting and your installer should measure that not listen to the boiler.

I think you mean your system is sealed but the cylinder is OV.

Tony

Tony, I have a new 428 and have been having great fun with cycling issues. However I can observe that if d.0 is set to 18 instead of default 30, the start up firing is much quieter (right from the start) than when it's set at say 24 or 30. I can only assume from this that d.0 does set the range and it is not kicking off at max power, which sounds like a damned fighter jet on the 428.
 
Mr Mod, more to the point is the heating load you have!

Whats the whole house calculated heat loss? Whats the load of all the rads?

It sounds as if your boiler has been over rated as well. Who specified it in your case?

Tony
 
Why not use a VR65 box with the boiler, then using dhw priority you can match your dhw load in D.77 and your maximum flow temperature in D.78. Added advantage of no time delay while heating dhw, and flow temperature in heating is set independently. Job done :D
 
Mr Mod, more to the point is the heating load you have!

Whats the whole house calculated heat loss? Whats the load of all the rads?

It sounds as if your boiler has been over rated as well. Who specified it in your case?

Tony

I have used the online heat loss calculator and get 18kw, but that's well at odds with a 2400sqft detached house on a hill, 26 windows, 18 radiators & 250L unvented cylinder, which does work out around 28-31kw. The rads alone are about 28 kw as some are beefy, but there are a couple of long runs as the house is long & thin.
The installer was actually suggesting a 437, but I thought the 428 would be sufficient.
 
Tony, I have a new 428 and have been having great fun with cycling issues. However I can observe that if d.0 is set to 18 instead of default 30, the start up firing is much quieter (right from the start) than when it's set at say 24 or 30. I can only assume from this that d.0 does set the range and it is not kicking off at max power, which sounds like a damned fighter jet on the 428.

My view is that if the calculation comes to 18 kW then thats whats needed.

Your own observations with the boiler indicate that its happier set to 18 kW as well.

So left like than how does it cope withheating the house and water?

Tony
 
My view is that if the calculation comes to 18 kW then thats whats needed.

Your own observations with the boiler indicate that its happier set to 18 kW as well.

So left like than how does it cope withheating the house and water?

Tony

Tony
Had one of the senior Vaillant engineers spend 2 hours today on the boiler & VRF430f.
End result is that it will run at max power without cycling, but the short run to DHW did mean that the auto bypass needed to be left wide open in order to maintain <30C delta between flow & return, which kind of jury rigs it IMHO. In the end he recommended a differential valve if it was a problem.
So far, no cycling. Eventually we did range the boiler down to 24kw on CH, 18 on DHW and will see how it runs. I will close down the ABV a little over the next week to see where it should stop.
 
@tommcdonna

The 430F has options for the control being Thermostatic or Modulating. The Vaillant guy recommended keeping it at modulating (rather than thermostatic as default) if you have 1 zone + DHW with a VR65.
 
Sorry it its stated before, but dont you have a lockshield balancing valve on the heating coil supply to use to adjust the flow rate?

Tony Glazier
 
Sorry it its stated before, but dont you have a lockshield balancing valve on the heating coil supply to use to adjust the flow rate?

Tony Glazier
@tony
If that comment was for me, why would I want *any* restriction on the DHW coil when I have a 22kw fast recovery coil ?
 

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