Best Of

I’ll tell you guys two stories about a stupid homeowner (couldn’t have been me!) with a modcon:

One cold February, they noticed the pressure relief valve was dripping. So they tried to reseat it by opening it and flushing it a couple times…. Which made it 10 times worse and then the leaking was filling a 5 gallon bucket once a day. It stayed that way for a week while the new relief valve was being shipped. Then the homeowner (swear it wasn’t me) drained more of the system than was necessary because they didn’t understand which shutoff valve was which (combo boiler with a domestic shutoff lol).

In another similar scenario, they had a leaking automatic air vent on top, dripping down the unit out onto the floor. Took about a week to get the replacement part and fix it again.

In both scenarios there was lots of makeup water being added to a boiler that is certainly sensitive to it. And after the second story, the homeowner learned that perhaps the feed water valve should not be left open year round. (That was year three of owning the house).

Anyway, I’m just a dumb homeowner, but I’ve done the math for myself. Based on a 15-20 year life of a modcon, professional maintenance at least every 2 years, initial cost, and current natural gas prices, the cost of ownership of a cast iron boiler with professional maintenance every 4 years and an expected life of 25-30 years comes out slightly lower. Theoretically.

Couple caveats would be that: having to repair or improve a chimney for a cast iron boiler would change things, temperature control on a cast iron boiler without ODR might be less granular (but also, aren't wives kinda like reptiles that like to be kept warm under a heat lamp?), you’re theoretically locking in your heating choice for your entire period of ownership (and maybe part of the next guys) while there are new technologies advancing and becoming viable, and a bigger chunk of the cost of ownership is paid to the gas company instead of a local HVAC company.

It’s not black and white, but I prefer things to be simple so I think a cast iron boiler is a better fit for me. But who the heck really knows until you live with for 30 years!

An $800 blower motor and blower wheel can eat up a bunch of fuel savings. Don't forget to add the labor cost and the mark up.

I agree once trained but if that training is not used yearly, monthly, weekly how much is retained.
I’ve had training on equipment that I did for 1, 5, 10 years. Yes I remember “Most” of it. Do I remember something I don’t use or used only for a short time. No!

i think the total cost of ownership might be a little better with the ci boiler on a high temp system due to the longer life but i have nothing against putting a mod con on it either. I was more arguing that a mod con had very clear benefits in simplifying a lot of the complication on a gravity or radiant system.

One of the minor arguments for condensing boilers is that they can run in condensing mode "most of the year" even on systems which need hotter water some of the time.

This is perfectly true. It is also misleading as to how much one is going to save, as perhaps I may be permitted to point out that "most of the year" the boiler won't be running that much, if at all, anyway.

Mind you, I am not opposed to a mod/con boiler powering radiation sized to the heat loss of the house and sized to operate on the low water temperatures, and controlled with an outdoor reset with indoor trim capabilities and variable capacity pumping and all the bells and whistles. Not at all. You can save as much as 10% of your fuel use that way, which can be significant.

Will it pay for the more expensive boiler and more expensive maintenance? Um… I am open to being convinced, but I can't make the numbers work.

are you going to be working on the boiler after it’s installed

Condensing boilers can save in fuel usage for 1/2 or more of the year depending on several factors. No if you have to pay for the repair and maintenance a lot if not all the savings can be lost.

Looks like you kept the closed spaced Ts from the original boiler. You either have closed space Ts or hydraulic separator, not both. With the way you have, you won't get much if any flow through the sep as all would just go between the two closed spaced Ts.

I would remove the closed spaced T and replumb the primary loop and also fix the ports on the seperator. That will fix all your issues.

The combi has an internal circ. There is no need for any extra circs beside the Alpha for the secondary loops.