PVI Boiler

I doubt that this was a problem with the boilers themselves. It looks more like an incoming water quality/treatment issue.

The system might also be a candidate for a tankless or "instant" gas-fired scheme.

a few reasons mainly apply here, as mentioned already poor water treatment or maintenance, the burners were more than likely not set up correctly and have been 'over firing' causing the damage, a simple thing would of been to down rate them, direct fired alternative is probabley better for your application

Cheers

Matty

What is the quality of the incoming water, and what water treatment regime is in place upstream of the boilers?

It is hot domestic hot water system and it is not treated. PVI boilers are known for this kind of problems. Tanks are small with lot BTU-s. They have fast recovery ( with in 5 min. heat water from 100 to 160 deg). Just looking to replace with some heaters that will last longer and maybe made with stainles steel.

Thank you all for reply's

Have the same problem where I work, every 3 years or so have to replace tube bundles. Noticed during the last install that some nonferrus material was used...they have copper tubes merged with a metal casing that surrounds the fire. Installed huge water softners, looked a year later..is a little better, today reopend boiler and found more corrosion where the tubes intersect with the metal shell. looking to install better boilers.