Pump to replace Alpha2 15-60 130, UPS or UPML?

I am still struggling to balance the system to achieve a 20C heat loss per radiator. And at pump speed 2 the boiler goes into S.53. Everything is fine if lots of zone are requesting heat. But the moment there are only 1 or 2 zone that need the heat my boiler is too big even at 18KWs.
 
Sponsored Links
I can tell you that once I installed the Grundfos 25-80 and set my ABV according to the instructions (in my case, 600mbar at ~1400 l/h) at a setting of 0.1, I know longer get S53 and the delta T is around 20 (slightly above depending on the d0 setting as per my previous post). I still hit S53 when a cold zone opens up and flushes the return with cold water, hence going for a LLH to eliminate that, and to allow me to use the boiler at full capacity (house heat loss is 34-36KW).
 
My boiler was sized correctly for a traditional system. Since installation we have done several things to actually reduce the heat loss. Also I use Evohome and never heat the whole house. That doesn't play nice with a big boiler.
 
Remember, though, that in a zoned system, the boiler will always be oversized. My heat loss upstairs may only be 18KW, but I still run my boiler at 34KW and it still maintains a delta T of 20 (ok, 21 to be exact). The problem is the 400 series Vaillant seems very sensitive to flow-return temps, especially on start up, because it doesn't modulate down quick enough. The new PCB may have helped with this, but what I've learned from my struggles is that minimum flow rate is key - and the only way to achieve this is to have an adequately sized pump to deliver this flow rate at the hex resistance inside the boiler and an appropriately set ABV to allow the water to circulate around the boiler fast enough.

OR - an LLH, which would achieve similar, and allow a smaller pump on the primary circuit (with an additional pump on the secondary side).
 
Sponsored Links
@fezster are you sure you are calculating d0 correctly. The reason I ask is d0 sets the max boiler heat output but if you can (And I can) measure the actual heat output, you will quite often see a heat output value lower than what you have set in d0 as the boiler modulates down. it could be that.
 
@fezster are you sure you are calculating d0 correctly. The reason I ask is d0 sets the max boiler heat output but if you can (And I can) measure the actual heat output, you will quite often see a heat output value lower than what you have set in d0 as the boiler modulates down. it could be that.

That is a good point, and you could be right. What I can say, though, is that adjusting d0 whilst the boiler is firing on a cold zone results in a noticeable change in the fan noise and in the delta T on d40 and d41, so it must be having an effect.
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top