Slick marketing by Vaillant but it leaves me wondering.

[Ed Sirett]

Hi all,

This week I put a 31kW Vaillant Condensing Combi in. The other month I put in a 24kW unit. As I was doing the job, I started to think is there _anything_ in the boiler that's different between the two units? I had sort of assumed they would be _almost_ identical but with perhaps a bigger fan, gas valve or burner/heatX.

Well I was showing my apprentice how you could find out about all the different settings. We looked up the fan speed when it was doing HW and it was 499 rpm, I was fairly sure when I commissioned the 24kW unit the fan speed was 395 on HW. Then the penny dropped, they are physically identical units to the last nut and bolt, except for a couple of bits in the firmware! The power is proportional to the air flow rate which is more or less proportional to the fan revs. 499:395 is very near 31:24.

I strongly suspect the 37kW unit is also the same (the fan will just go yet faster). I did a 28kW unit about 12 month ago and that ran to the mid

400s on HW.

Part of me is truly impressed with the design which makes a whole range of models from the same production line. Part of me is wondering by what mechanism can a the huge price differentials be maintained ( £815 versus £1009) for essentially a firmware difference.

I suppose some people would say buy a 30kW boiler from someone else who could potentially be cheaper for the higher powered models.

In Hong Kong there is probably someone who sells grey market chip upgrades...

[Ian Stirling]

But are they CORGI registered? :)

[Andy Hall]

Why does a dog lick its parts?

The large computer manufacturers did this for years, some may still. IBM is reputed to have had a DASD (disk drive to everyone else) upgrade to improve the data rate. This consisted of two pullies and a belt and the customer was neither allowed to see the upgrade kit or the installation of it "for intellectual property reasons". Cost was some way into four figures.

[Andy]

Surely the heater exchangers must be different from model to model, as the flame temperature and loop temperature are fixed? Unless, that is, all the lower power models have oversized heat exhangers and have an appropriately restricted gas flow.

Andy.

[John Rumm]

Much the same way as a Mini One can be turned into a Cooper with a software swap and yet the price differential is still maintained. The average driver/fitter is probably not well enough clued up on these things to cause a problem for the makers on a large scale.

How is the firmware held on the boiler (i.e. EPROM, Flash etc)?

I was thinking more like a quick download from the 31kW one! ;-) (at least that way they could not say you were not using genuine firmware)

[Owain]

Then ask yourself how long a 28kW unit will last when running at 37kW?

Intel manage it and AFAIK they don't even change the firmware, just disable bits of processor. Zap! and the power is gone.

Owain

[Fred]

I would think it will be a combination of fan speed and burner pressure. Is everything else identical? One way of checking would be to look at the spares list - I assume they have one.

What sort of fan motor is it? What determines fan speed? I presume it's not a modulating boiler.

[Guy King]

The message from Ed Sirett contains these words:

I forget which computer firm it was in the 60s(?), perhaps ICL, that had a simple upgrade to double the speed of your computer. When the firm paid for the upgrade a technician arrive, took off a panel, snipped one wire, and put the panel back.

[Andy Hall]

Designs vary though. For example, on mine (MAN MIcromat), there are different sizes of heat exchanger for different rated outputs together with a different component where gas and air are fixed before passing through the fan to reach the burner.

The output is then entirely controlled by the fan speed, the fan being a motor with servo operated by the boiler controller. The gas pressure, if it were measured at the output of the valve is around zero. The combustion adjustments are via two controls on the gas valve which are used for the top and bottom ends of the modulating range. Adjustment is made against CO2 percentage in the flue gases.

Via this method, the boiler can operate over a 4 to 30kW range.

Viessmann and others use a similar design.

Given that, it's entirely possible to have a single mechanical design which will operate at up to 30kW or so with soft limits in between.

To some extent, even if there is a larger heat exchanger for larger models, the difference in manufacturing cost, even multiplied by margins in the distribution channel does not add up to a £200 difference. If the only mechanical difference were a diffierent injector, it wouldn't either.

The point is that the products are positioned at the market price for the capacity and functions of the boiler, taking into account brand value as well. As a result, Vaillant will make more margin on the higher end product and less on the higher volume smaller ones. Production and material costs are only a part of the pie.

[The Natural Philosopher]

I got paid a couple of hundred to do the same thing to a guitar amp I had designed once.

The customer wanted the chorus to 'sound like a Roland, not like a Leslie speaker'..it had taken me a week to design it to get rid of the harshness of the Roland sound..using an all pass phase shifter. I simply snipped one wire on the capacitor..

[Doctor Drivel]

Matt, why should they be? Motor makers have done this years. The BMC A series engine block was used in 700cc to 1300cc engines, although with heavier cranks and different cly' heads. Same block though. heat exch = block. Some mods here and there and a new model with different performance to add to the range.

[Doctor Drivel]

It modulates but Ed said the maximum is clipped on lower models. You will most prob find the same instruction manual for all models and the only different part NO. is the pcb. See if the heat exchanger is the same part No for each.

[Doctor Drivel]

What is the max kW and fan speed on CH? They have obviously changed matters for DHW.

[Ian Stirling]

If the only difference is in fact the firmware, as it may be, as long as the 37Kw stamped one.

[Fred]

So if all else is equal you can upgrade for the modest cost of a PCB!

Reminds me of an early Amstrad satellite receiver. There were 16 and 48 channel versions with a substantial price difference between them. Yet the price, until Amstrad got wise, of the relevant IC was a few pounds! Most independent retailers would happily modify your receiver!

[Fred]

You're actually partly right here. The Mini (and variants) used 2 blocks which were rather different. The lighter one was used for the 850 to 1100 cc varieties and the other for 1275 and Cooper engines.

There were other A series engines such as 803cc but they were inline engines and slightly different again.

[Bob Eager]

IBM. ICL wouldn't have had the nous.

[Andy Hall]

I once worked with an engineer who had been involved ina previous life in the design of TV sets at Plessey/Philips/Pye (I think the place was each of these at one time or another). At any rate, the chief engineer would go round with his wirecutters looking at the proper designs and would snip out components until the set stopped working.... Apparently, considerable cost savings were made this way.

[Ed Sirett]

That latter description is exactly how they work, AISI, because they are condensing units the greatly over sized heat exchanger for the lower end models is not a problem.

The matter was a particular irritation to me as I bough the 24kW unit the other month mainly as a heating unit with the HW side just for an adjacent WC basin. I was vexed to discover the heating side is pegged to 19kW although the HW goes to 24kW. The setup parameters allow you to further restrict the heating but not to increase it.

[Ed Sirett]

Once they are out of the guarantee period the only obstacles would be legalities of making such a mod. Setting that matter aside there would be changes in the maximum permitted flue lengths (almost certainly not an issue) and the sizing of the gas supply pipes (almost certainly an issue in most places).