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.
Vaillant EcoTec 428 configuration issues for Hot Water Only
- Thread starter tommcdonna
- Start date
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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In physical appearance it looks exactly like this one:
http://www.screwfix.com/prods/34127...ols/Honeywell-Straight-Auto-Bypass-Valve-22mm
I don't know if there are several different models that look exactly the same, but if not, it's defintely 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.
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
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).
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
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
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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 
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.
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.
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.
@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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