Which fan?

The Potterton Suprima has a fan problem, although its not a technical problem. The Suprima fans are as long-lived as any other bother fan. The problem is there are so many almost-but-not-quite-identical fans fitted to the various versions and sizes of Suprima, that when buying a fan it is very easy to buy the wrong one. You are totally reliant on the merchant or the website supplying the correct variant for yours and as you can imagine, the chap in the merchant or the website does not always get it right! So while physically changing the fan is reasonably straightforward, actually identifying and buying the exactly right fan in the first place, certainly isn’t.

So which one out of so many fan part numbers out there is the right one for your Suprima? You can look up the the part number in the manual for you’re particular Suprima but the merchant or the website will probably tell that part number is obsolete and you need <some other> fan. They may or may not turn out to be offering you the correct fan but you won’t find out until you’ve dismantled your boiler, removed the old fan and offered up the new one you’ve bought. In my experience the chances are about 50/50 the newly purchased fan will be subtly different and won’t fit. 

So how does one identify the correct fan? In my experience this can be done by looking at it, ir if buying on line, looking at the photos. There are three features of Suprima fans that need to be noted on your particular boiler fan. The motor power, the number of fixing screws and the width of the fan backplate. 

1) Motor power. This can be 48 Watts, 58 Watts or 72 Watts. There will be a data label attached to the motor telling you the motor power (along with a few other details). Here is the data plate on the motor of an old fan showing a motor power of 58W.

2) Fixing screws. Some fans have three fixing screws through the mounting backplate, others have two fixing screws and a lip under which the backplate engages. The two types of fan look similar but are not interchangeable. Here is a photo showing the three fixing holes on a three-fixing-screw fan. On a two-fixing-screw fan the top screw hole is not there, and the top of the fan backplate engages under a metal lip. The two-screw version looks the same at a glance but with the top hole in this photo missing. I’ll find and post a photo of a two-screw version for comparison one day, eventually, perhaps!

3) Backplate width. All Suprima fans have look roughly similar and they all have two fixing screws along the bottom edge of the backplate, but the backplate itself comes in two different sizes/shapes. The two shapes look  almost the same and the way to tell them apart is by measuring the width of the backplate, as in this photo. Measure along the bottom edge by the two lower fixing screws and you will find yours is either 6 1/4” wide or 6 3/4” wide.  Make sure the new fan you are buying is the same width backplate as your old fan, or the screw holes will not line up when you come to fit it.

So for anyone replacing a Suprima fan my best advice is read the data plate on yours to establish the exact model of Suprima and ask your merchant to look up the correct part number, but take your old fan with you to the merchant and compare the three features listed above with the new fan you are offered to make sure all three features exactly match. Here is a photo showing where to find the data plate telling you the exact size and model. (On this photo if you zoom in you’ll notice another trip-up. This boiler has had a new PCB and chassis fitted and the installer didn’t bother to fill in the new data plate. Leaving it blank like this is very unprofessional but sadly very common. If yours is blank, the boiler can usually be reverse-identified using the fan features described here on this page and the size label usually on the gas valve.)

I abbreviate these features above as 2S or 3S for the number of fixing screws, NB for 6 1/4” narrow base backplate and WB for 6 3/4” backplate, and the motor power in Watts (W). E.g. “2S NB 48W” is 2 screw, narrow base, 48 Watt motor. So here are the five different formats of fan I’ve seen in Suprimas so far, and all of the many part numbers of fan in circulation seems to fall into one of these five categories.

2S NB 48W 

2S WB 48W 

3S NB 58W 

3S WB 58W 

3S WB 72W

A quick note about the low priced clone fans on the market. Most are 3S NB 90W format, and the 3S NB backplate allows this fan to fit the most common models of Suprima but the motor power is 90W, far more powerful than the correct motor. These seem to work perfectly well when fitted into a suitable boiler but with the extra motor power I’d expect more air to be drawn through the combustion chamber than necessary resulting in lower fuel efficiency. This will translate into higher gas bills.

If you'd like me to fix your Suprima, call or text me on 07866 766364.

Mike the Boilerman

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Three-fixing-screw Suprima fan

Measuring the Suprima fan backplate width