HB Smith Cast iron residential boiler tripping out on rollout switch

kappy24

I have a natural gas smith cast iron boiler (GB-100) that is tripping out on a rollout switch located above the burners. I’ve brushed cleaned the heat exchanger, cleaned the burners, removed the flue piping and inspected the chimney to make sure it’s drafting and there are no blockages, replaced the pilot assembly and thermocouple. I’ve even replaced the rollout switch rated for 350° and the boiler will run but will not satisfy and trips out due to excessive heat by the manual reset rollout switch. Asking for help on what to do next to get this customers boiler working again, Thank you. 

EBEBRATT-Ed

Either you putting too much gas into it, the boiler or flue pipe is plugged with soot or the chimney is not drafting.

Look up inside the chimney for blockages, the tile in the chimney may have broken down.

But a draft gauge on the boiler flue and see what you getting for draft. That boiler has a built in draft hood I think.

kappy24

I made sure the chimney was drafting and the flue pipe was completely clear. The gas pressure is spot on 3.5” w.c. The boiler does have a draft damper but I can watch the damper open up all the way and hit the end switch starting the  ignition sequence. I suppose I can get up on the roof and look down the chimney just to be sure from the top down.

would turning the gas pressure down or trying to adjust the combustion air on the burners fix this issue? 

EBEBRATT-Ed

@kappy24

You can probably safely lower the gas pressure to 3" wc but you need to use a combustion analyzer.

If the fire is rolling out you have to find out why.

If you pour water into a funnel and it overflows what do you do? Pour faster or slow the pouring down? Same thing

What is your draft reading? You have to use a draft gauge and an analyzer

mrfyvie1

HB Smith GB100 approx 19 years old never had a problem. now I have the same problem. Boiler heats up, but trips the Thermal Cut-off( roll out), above the burners, before it's satisfied. Flue appears ok, and I also have a gas water heater venting out the same chimney, with no problems. I have replaced the roll out switch, to no avail. I was wonering if it could be the Honeywell hi temp shut off. I could use some help……please…..Mark

Jamie Hall

To be clear — is this the rollout switch from the firebox, or the spill switch at the flue? Very different problems…

Probably be a good idea to get a tech. to clean the boiler and check all the combustion parameters…

mrfyvie1

Roll out switch from the firebox

delcrossv

https://forum.heatinghelp.com/discussion/comment/1666514#Comment_1666514

This. ☝️

Jamie Hall

And it's past time to get someone out there and thoroughly clean the boiler, check the flue, adjust the gas pressures, adjust combustion…

Can't be done by eye.