Gas Slant/Fin Boiler Shut Off Before Thermostats Programmed Temps are reached

broth

Old school gas SlantFin was working fine. Recently, the boiler runs for a short time and reaches its temp which must be set at 140 and shuts off. I have a 2 zone system(upstairs and downstairs). With current issue sometimes hot water does not run through the system and sometimes it does. Rarely will the individual thermostats reach their set temperatures. Definitely seems to be a worse problem overnight but really happens all the time. Had someone in who thought it was a zone valve issue. Replaced it, with no positive change. At first, I though it fixed the issue, but it did not. This morning woke up to well below thermostat low temperatures both upstairs and downstairs. Boiler temp appeared at right around 140 , but no hot water running through the system. All baseboards were cold. Turned the system off and on. Boiler kicked on for about 5 minutes. Temperature went down initially and heated back to 140 and turned off. Any ideas?

Jamie Hall

Well, the first question I guess is did you make any changes to the system more or less when you noticed this starting to happen? If so, that's the first place to look. Undo the changes and see if it goes back to the old way, then figure out why the changes make it misbehave.

Beyond that. What thermostats are you using? Do they require batteries? Are the batteries fresh?

Do the zone valves open (I'm presuming zone valve type control) when the corresponding thermostat calls for heat? If not, it's as likely to be a problem with the thermostats or their wiring as it is to be a zone valve problem.

Do the thermostats also control the circulator? Or is the circulator controlled by the zone valves? If the former, there must be a control board or relay or two -- are they working? And an obvious question, but sometimes overlooked: is the power supply to the circulator OK? If the circulator is controlled by an aquastat, is that working properly?

At some point you will need to determine exactly what controls what in your system; this would be a good time to figure that out.

EBEBRATT-Ed

also check the water pressure on the boiler gauge. It should be 12-15psi with the boiler coo/warm and not over 22 when hot

HVACNUT

If the zone valves are open and the circulator is running and the boiler is making limit, then it seems there's air in the system. Do you know how to purge?
Post some pics of the boiler at different  angles from 10 ft away. 

broth

Thank you for the responses. Everything was working fine until the past week. As mentioned the tech came in and said one of the zone valves was not opening and closing properly, so that is why it was replaced. I thought things were working ok when he left, but I was wrong. I replaced the thermostat batteries before the tech came over. The aqua stat was changed last year. Everything worked great last year and the first month this year.

Water pressure on the gauge runs higher than 22. In fact, goes up to about 28psi when hot. What does that mean when it goes that high?

I was thinking that air in the system could be an issue. Although, I am not hearing any knocking. I have been researching how to purge and will look to try that.

Zone valves seem to be working.

Tonight, I came home to both levels of the home at their set temperature. Very confusing that the system behaves so differently throughout the day.

neilc

HVACNUT said:

Post some pics of the boiler at different  angles from 10 ft away. 

show us the expansion tank, or compression tank,
and the circ(s),
and the valves

HomerJSmith

What thermostat do you have?