Grundfos Alpha 2L Proportional Pressure

[fezster]

You really need to take readings as close together as possible, otherwise you are just averaging. Temperatures are easy, d.40 and d.41 provide the info. Unfortunately there is no equivalent for boiler output, so you have to take gas meter readings. 2 minutes apart should be sufficient, but wait until the boiler has stabilized, i.e temperatures are constant. (d.34 gives the fan speed, which controls the output, but Vaillant don't publish a conversion chart.)

I believe later versions of the 4XX boilers have a revised PCB which doesn't restart at max output. My boiler (not a Vaillant) always restarts at min output, then ramps up if necessary.

Yes, I have the revised PCB. However, it definitely still starts up on "full" output. Someone previously mentioned it works on a %age of d0.

I'll have a look into d.34, see if I can correlate it to gas consumption. Would certainly make it easier to take readings.

 

[fezster]

I thought I'd update after having the LLH fitted. After some careful balancing, the Alpha 2L is indeed good enough for both u/s and d/s, which I'm pleased about. This is in PP2 mode.

The DAB VA 65/130 is being used as the boiler shunt pump on the return. It's spec sheet quotes ~4.5m head at 1.66m3^s, so I'd have thought would be sufficient for the 438. However, it gives me a 22C delta at 34KW (this is what my requirement is). I'm guessing this could be because the pump is approx 5 years old (reduced performance?) and the boiler hex probably isn't as clean as it should be. Perhaps some X400 at some stage may help.

Anyway, I'm happy that it's all working as intended.