I'm going through the process of replacing a Baxi Bermuda 552.
NOTE: Currently I only have a single Filler/Expansion Tank in the loft... if you have that, you probably have a Primatic Hot Water Cylinder
I hoped I could just replace the 552 with the Baxi BBU15HE.... the Baxi literature does give this impression... although this is true... it's not the whole story
Because:
1. I have an old Primatic Hot Water Cylinder which can't be connected to the new BBU15HE (the Primatic is Gravity Fed and the BBU15HE won't connect it's PUMPED feed to this).
2. the Gas FireFront (which my wife loves) needs to have a connection to the chimney for Hot Gases... guess what? the BBU15HE has no flue connection for the old Baxi Gas Firefront. I would guess that there would be a problem with the coldish gases from the BBU15HE and the hottish gases from the old Gas Firefront.
So, as well as a BBU15HE and Concentric Flue, I am buying a new "normal" "pumped feed" Hot Water Cylinder plus a Baxi/Valor Dimension FireFront (it's basically at 2KW Fan heater), but has a nice 3-D fire effect and a Remote Control (for the fan heater) and has the Boiler Control (Reset and On/Off) too. You don't get a BBUHE15 Boiler Control panel with the Boiler... it comes with the FireFront! And I will need a second, small, Expansion Water Tank for the BBU15HE.
So Baxi are not telling lies of course (the 552 CAN be replaced with a BBU15HE), but they could be more realistic in what the customer needs to know (such as not being able to have a Gas Firefront and not being able to have a Gravity-Fed Hot Water Cylinder.
My solution involves a slight change to the pipework (not a lot actually, and no floorboards needs taking up, thank goodness) and a Hot Water Cylinder Thermostat twin cable fitted from Cylinder to new Boiler. (I've removed the plaster architrave around part of the front room ceiling... the twin cable will be fitted in the gap behind the architrave... and then through a small hole through to the Hot Water Cylinder).
Oh, one last thing, we decided we would still like a gas fire in case of electric power cuts... we've invested in a rather nice Butane Gas "Stove"
With Primatic systems it's advised NOT to use preservatives in the central heating as this could migrate into the hot water coming out of the taps. Once I have updated my system, I will be able to add Flush or Inhibitor to the new small Expansion Tank.
I hope this helps someone who is as confused as I was a week ago.
Roy Marsh, February 2010