I'm not in the HVAC trade but I've de-bugged and repaired my share over the years. I design and build electronics, from very simple to very complex. When trying to understand and repair someone elses design, sometimes its best to strip it down and then slowly add components/features back, one by one, until something doesnt work right.

I dont know if you have a separate thermostat on every zone, but if you do, then I'd suggest unhooking them all. Let the radiators cool down. Then hook one up at a time, and confirm that its radiator(s) are working as expected. As a matter of fact, check them all- even the ones that shouldnt be effected by the test. You should come to a point where the zone being tested, isnt being controlled properly, then you can focus on it.

If you only have one digital/programmable thermostat, you should probably power it down (unhook it from all sources of power) and then re-connect, to re-boot it. Maybe reset to factory defaults, if its user manual explains how.

I have a 7-zone hydronic system and thats how I would begin, anyway.

-NC

can you post up a photo of your system? What kind of boiler is it?, model number and brand. You mention you have old cast iron radiators. Did they use rhomar system cleaner? Does the system have a strainer and a high efficiency air purger? does it have proper pumping away principles? 95 percent of problems with new systems are installer related.

Sounds like your boiler system is smarter (higher tech) than your service folks. Probably something simple but if they have not figured it out after 5 or more trips, sounds like it is above their pay grade.

If I understand correctly, you have 1 stat, 1 circulator and a flow control valve that is manually set to open due to it is sticking closed causing previous circulators to burn out. The open flow control valve is usually closed and opens when pressure from circulator pushed water through.......should be closed otherwise unless circulator has a built in one (IFC). The water feeder was likely replaced because it may have been sticking and not adding water when it was supposed to......but when the system is already up to pressure it should not be needed. By description of faults noted, the system is gravity feeding on off cycle so some radiators heat.....usually the closest to the boiler and supply header heat with out circulator. You usually won't have much air lock problems on a cast iron radiator system because they are high and capture the air while still allowing circulation. Modern installations are piped differently. Pictures would definitely be helpful.

I wanted to be sure I was clear, an open flow check will cause gravity heat......heat without a call from the thermostat.

It might not work, but, it looks pretty.

Was it designed by Italians?

Can you show picture of flow check and piping around boiler?

that amtrol air purger needs to have at least a 18 inch piece of straight pipe for it to work properly. I would relocate the pump to the supply side and bring the makeup water into the bottom of the air purger because that is the point of no pressure change, it appears that you system may be a monoflow system. If that is a filltrol tank, I would ditch that and go with a B&G pressure reducing valve and a number 30 tank. To be fair boilers were installed that way for years but newer methods work better.

This is piped according to older piping instructions, probably for ease of boiler change out for the installers. I am not a fan of that loop back on the supply piping where the expansion tank is.......in my opinion that is quite a bit of friction loss (pressure loss) to circulation. I believe that I would have eliminated that reverse bend in the piping.........but that what I would have done and does not mean it would not work properly. Also, I would have installed the circulator on the other side of the expansion tank, pumping away from the tank for the best circulation pressure on the circuit. I DO NOT want to pick apart the work of another HVAC person......just adding my 2 cents. I am curious to how the system is set up......such as 1 perimeter pipe with a supply and return from each radiator after the flow check?

Right you are RandyT!

I would have replaced that flow check......just because of age. It is like have new shoes but using old laces.

I would have too, but instead I would have probably used a Grundfos up15-58 pump with a built in check instead. In light of the old piping and radiators, I would have used a system cleaner, probably a rhomar product

Lennox GWB8-075E-3

I am no way a expert and this is probably not the problem but does it hurt the efficiency of the system to have that new smaller diameter copper pipe feeding into the bigger diameter steel pipe?

Or is it just deceiving on size of pipes?

My thinking is that might be a problem area for air filling the pipe and not bleeding off properly.

That old red flow control thing above the Boiler, is original to the house . House originally had a coal fired boiler with an indirect water heater that the Boiler would heat . They got rid of that after they switched to a gas fired boiler, and gas hot water heaters. The red flow control is the thing they set into a permenant open position, so the circulator pump would not burn out. That old flow control must be at least 100 years old.

I would have piped the supply straight up from the boiler then over towards where the flow check is. Then horizontally, I would have installed the expansion tank and feeder as Randy T has said. Then after the 90 elbow would go the circulator and flow check before connecting at the first cast 90 elbow. Isolation flanges on circulator and ball valve vertically above the boiler supply port. With a large supply main, there can be circulator short cycling due paid temperature changes as the cold in the main returns to the boiler.......just an observation.

The flow control is supposed to be closed to prevent gravity heating........that is its function. If it is not working correctly then it should be changed.......like on the service call that they decided to leave it open.

wonder how many btus the new boiler is, looks like 1 1/4 copper which is only good for around 130 thou btus. I'm not familar with that brand, it is probably made by a boiler manufacturer for lennox, maybe dunkirk. Beings it has cast iron radiators perhaps a bypass is needed at the boiler to prevent to cool of water coming back on the return. The nice thing about the grundfos up 15-58 circ is it is three speed and the speed could be adjusted for a 20 degree differential. I'm sure they will get to the bottom of the problem, it does them no good not to.