I've fitted about twenty five now and haven't had a call back on any of 'em. They are easy to fit and you can get the pipes up the back without any spacer kit. The jig and flue positions are interchangeable with the Baxi 105e / HE/ and Main 30HE so if you are replacing any of these with a Main 30Eco it's a cinch. They are aluminium silicate so not the same as the Duotec (which is stainless) but the rep tells me they are bomb proof and the heat ex. is taken from a tried and tested industrial unit..... but then he would, wouldn't he.
Actually the rep is brilliant, drops me free parts off occasionally and has given me hospital kits for both band b he and band a eco boilers free of charge. He also organises the odd bowling night out for the lads (and lasses) from the local merchants. If you register with Main you will get a two year warranty as well.
I've done three or four training days at the local Baxi training centre in Warrington - haven't had to pay for any of 'em, in fact I've got a Duotec training day booked for next month, again gratis.
Overall, if you need a budget boiler Mains are great, if you need something a bit more powerful or refined a Duotec is the one.
Dan
