Range rating by fan speed

[JonathanM]

For my new boiler I'm wanting to keep my open vent set up, I want decent modulation, and I'd prefer to have a stainless steel heat exchanger. Also, I want some basic options to facilitate cool running, like adjustable anti-cycle and ramped power increase. And very important, I want to be able to range rate it. I keep checking out the Alpha regular boiler, which seems to have all of this.

The problem is that the instructions for range rating are somewhat opaque. I spoke with Alpha technical support, with two very nice guys. With the first one we seemed to be talking at cross purposes, until I finally realised he didn't seem to know what range rating was. He passed me to his colleague, who knew what it was, but said nobody did it any more because of modulation, and that nobody had ever asked the helpline how to do it. Anyway, he read through the relevant bit of the manual, and seemed to think it could be done. I'm used to reading about boilers where you can choose the power output by percentage. But Alpha only list the fan speeds. And, unlike Vokera, they don't give you a helpful graph which relates fan speed to KW. I've been told the fan controls how much gas and air mix is drawn through the burner, and it effectively controls the power output.

I'd be grateful if anyone with experience of this sort of thing could have at quick look at these instructions and advise whether range rating is actually possible. Also, I don't understand why the default minimum fan speed is 1400 rpm, but you can take it all the way down to 900 rpm. I would have thought the minimum fan speed would be set to 900, by default, so that it would give the best modulation.

 

[DP]

On vaillant Ecotec plus, d0 let’s you set the heat output to match the radiator load.

 

[JonathanM]

On vaillant Ecotec plus, d0 let’s you set the heat output to match the radiator load.

I was a little surprised that the modulation wasn't better, and I'm a bit in two minds now about aluminium heat exchangers as there is so much conflicting information. The 24KW Vaillant goes down to 6.1KW, but the 25KW Alpha goes down to 4.3KW.

 

[Harry Bloomfield]

I was a little surprised that the modulation wasn't better, and I'm a bit in two minds now about aluminium heat exchangers as there is so much conflicting information. The 24KW Vaillant goes down to 6.1KW, but the 25KW Alpha goes down to 4.3KW.

I ended up with an alloy Vaillant, not realising there were differences in HE's.

 

[DP]

I was a little surprised that the modulation wasn't better, and I'm a bit in two minds now about aluminium heat exchangers as there is so much conflicting information. The 24KW Vaillant goes down to 6.1KW, but the 25KW Alpha goes down to 4.3KW.

Estimation of heat load- allow each rad to be 1.5kw
You are unlikely to have three radiators, so lower figure may not be that important. Open to opinion of others

Alpha in its heyday was good, now I avoid this boiler (same applies to some other makes)

 

[JonathanM]

Alpha in its heyday was good, now I avoid this boiler (same applies to some other makes)

I know they have a variable reputation. That will be a big factor when I finally decide. That's going to be a very difficult part as there are so many views. Of the installers I have tried so far, one refuses to fit Worcester Bosch, and another says he's stopped fitting Vaillant, both for reliability reasons.

Estimation of heat load- allow each rad to be 1.5kw
You are unlikely to have three radiators, so lower figure may not be that important. Open to opinion of others

I have eight radiators on the downstairs circuit, and I think they work out at pretty much at 1.5KW each on average, like you say. So that's 12kW at a dT of 50. I don't really use upstairs these days. But I would be hoping to run it all very cool most of the year, with a dT more like 20. So I think that brings the radiator output down to more like 3.5KW.

 

[JonathanM]

One odd thing that has just occurred to me is that, on the face of it, there doesn't seem to be anything to stop you buying the 15R, and then increasing the S3 setting, to make it work like a 25R, thereby saving £250. It reminds me of overclocking computers, many years ago. I can't believe it actually works, though.