Main 15 He Boiler overview 

Clear and concise explanation. 👌🏻 Thank you.

Nice one doc......👍 . Pretty bullet proof boilers , funny enough I serviced a Suprima for one of my customers last week that I fitted for them 23 years ago and it's still working perfectly good , it's only needed 2 fans and never had any issues with the dreaded Suprima pcb problem....😜 happy days . Cheers.....👍

Interesting video. The reason this boiler is rated B rather than A efficiency is the standard set up of an atmospheric burner and (probably) a constant speed high temperature fan extracting from the primary cast iron heat exchanger imo. The fan will dilute the hot gases from the burner flame with useless excess air so cooling down the heat from the burner going into the heat exchangers, especially so if the burner modulates down from full fire like the old Potterton FRS38 boilers ** used to do (which had a copper tube boiler and no secondary heat exchanger btw). Modern condensing boilers have a burner similar in performance to an industrial gun type burner with a variable speed fan so that excess air is far better controlled especially when the burner modulates down to low outputs (there is no `extract fan' required). ** Interestingly the FRS38 had no fan proving differential pressure switch as far as I could tell (there was one installed in my late Grandmothers flat). The fan was very reliable, however if it did fail I think the idea was that the pilot light would eventually snuff out due to lack of oxygen and then the gas valve would lock out.

Very interesting for a relative noob like me. Thanks for the upload. Much appreciated doc

Its also marketed as a Potterton Suprima HE, dont see too many of them now. It was a favourite of house builders so you get whole housing estates where they are fitted.

Interesting - thanks.

Great video 👍

So I have this very same boiler, 8 or 9 months of the year runs like a charm, then come September October it starts tripping the main RCB, have tried it on 2 different power boards on different circuits same issue. Boiler seems to get up and running then a few minutes later the RCB trips. Happens first thing in the morning when hot water is requested at 4:30am and then sometimes (but less often) in the afternoon around 4:30pm when the evening water is programmed, doesn't seem to matter if it is the hot water or heating circuit that is requested. Secondary heat exchanger, fan and shroud, flu kit, air sensor and control board and 3 way valve were replaced 2 years ago as the secondary heat exchanger had a small hole that rusted some stuff. But as I say runs like a charm for the late spring, summer and early autumn months not one trip, then for the last 3 years late autumn and winter trips the RCB several times a week (not every time) a few mins after start up after not running for a few hours. Guessing something is condensing in the casing and tripping the electors when something a minute or 2 into the start sequence occurs. Any ideas?

So may I ask is this Main boiler with cast iron main and aluminum secondary heat exchanger a direct forunner of todays new design condensing boilers. Only I thought about this design to recover flue heat on a standard type boiler around 1995. However, at that time I couldn't find a heat exchanger to fit onto the flue, today they are everywhere. Kind regards Dave Porter

Lasts longer than all modern boilers and probably can be repaired with nothing but basic hand tools , great british engineering at its finest but hey we need 90% to keep saqid happy 🙄

Is there any way to tell if something is in a dry or wet pocket before taking it out?

sadly they don't make them like this anymore. b rating on energy consumption but it lasts for 20+ years and is easily recycled. an a rated condensing boiler might be cheaper to fuel but after 10 years you end up with a pile of scrap plastic, rubber, metal and circuit boards, half of which had to be replaced 5 years in you end up with a boiler and a half of junk

Very well explained. Tell me, why do they not make heat exchangers from Stainless Steel? Would that be less effected by the acidic condensate? Thanks for sharing.

Why do they put core plugs in the secondary heat exchanger? Great vid as usual mate. Also i have on old Rothenberger freezer like yours if you want it for spares board is fried.

You should try and restore it Dr pipe ;)

Wert the the first condensing and they just altered suprimas to suit it