Almost had Meltdown!!!

[chew72]

Well I definitely have no one to blame but my self. 😔 I've been running the boiler with no dump zone and meaning to install it before winter. I hadn't worried to much about the boiler because im almost always home and can run a generator to keep the power on if it goes out.

I've had a few fires in the boiler the past couple of weeks and today I made one to take the chill off. About half way through the burn I had to run out for a hour. I guess right behind me was the power company and they were replacing a pole on our street. So I get home and the power has been out for 45mins. I get then generator running, fire up the boiler to see a water temp of 256°F and yes the water was boiling. Below is a very close to scale drawling of my setup. I didn't add the air vents to the drawling but they are there. (Also the green pipe isn't installed yet.) As steam let off the hot water out pipe it was getting gulps of water back keeping things from running dry.

So.. 1st Question: What I want to add is a pipe (The Green One) as a way of the boler thermosiphoning in the event of a power outage or pump failure. I already knew the boiler does not thermosiphon very well if at all through the thermostatic mixing valve. The boiler is rated as 104 kbtu and the existing piping 1-1/4" I was going to make the green pipe 1" it will only be about 6' long. Then reading up on it they only need to be 10% of the boiler capacity. I'm now thinking 3/4" is all I need. It's cheaper and I may already have the material. 3/4" for 6' will flow quite a bit and 10,000 btu is all i need to move. The typical tank temp is 160F on ave, the bottom 1/4 is almost always 110F and the top never above 180F. Anyone else think 3/4" is large enough?

2nd Question: Swing check valve in the green pipe, or N/O Zone Valve? I already have a 3/4" N/O Valve. I like the simplicity of a swing check valve but my only hesitation with it is when the boiler pump stops and i'm pulling from storage, the return water will also run through the boiler and mix with my hot storage water heading out. I do automation and control and could have the valve cycle every 24hr or once a week and alarm if it's doesn't change state. Thoughts?

 

[salecker]

I have 1000 gallons storage and have zero issues when the power goes out.
I had a 5 hour outrage shortly after filling the boiler on the second year of operation. The boiler shut off and temps never climbed.
It may be in the way you have your sytem plumbed up
From what i have read over the years,storage eliminates the need for a dump zone.

 

[chew72]

I agree. How is your boiler protection plumbed though. I know the combo units that have a mixing valve and pump all in one also have a swing check built in. That's the key thing missing in my case.

I call it a dump Zone but essentially is treating the storage as a dump Zone.

 

[salecker]

I have a near boiler pump for boiler protection.
No mixing valve.

 

[chew72]

So I talked to a few plumbers I know and they all said 3/4" is large enough. I decided to go with a zone valve and ordered one online as they apparently are getting very hard to find, and no one had stock. Everything is on backorder here. Once installed I'll test it

 

[Smoothride]

A thermal syphon will not open a check valve. Nor will it go through a non operating circuit pump.

 

[flyingcow]

Ive got a solo innova 30 plus storage.

If i understand everything you posted you were asking for input on overheat when power goes off and boiler is in mid burn.

Above my boiler i have old fin tube up high on the wall. I used twice as much as recommended. That loop has an automag zone valve to the loop that stays closed when power is on. Power off the valve opens and dissipates the heat. But if you got a good windy day your fire will still keep burning. Might even dump out the pressure relief.

And ive had a few of these events. And IMO if the boilers still cooking good ill leave it off once the powers back on. It can get pretty noisy and shock the heating system when you start circulating steam/water. At times it almost seems to be a bit violent.

Good luck

 

[chew72]

I've ordered a 3/4" N/O zone vale. I'll install it once it arrives. I feel confident the thermal syphon to storage will be more then enough to handle any power outages.