I converted the tankless coil HW in my old (1975) American Standard oil fired boiler to a variation on indirect HW (with help from a friend who used do plumbing for a living). Reason was the coil wasn't producing HW rapidly enough, probably due to scale reducing heat transfer. I was going to put a new one in and was advised that some of the bolts were pretty rusted and it has happened that the boiler is damaged when trying to remove the old coil. The solution, although more expensive, was to add an insulated HW tank w/ a thermostatically controlled circulator that runs through the tankless coil. So I basically have a 40 gallon HW 'capacitor' which gives me enough HW. The set up has worked great for about 10 years but this morning I was running out of hot water. A hand on the coil output to tank was luke warm but is usually too hot to hold on for long. So it appears no circulation. Ass uming the tankless coil hasn't plugged, it can only be a problem with circulator or aquastat. Would my first step in trouble shooting be to bypass the aquastat and see if I get circulation?

Hi all, I'm new to the forums but glad to see a great community here. We moved into our new (but old, 1913) house in north suburbs IL last fall. Here are the heating stats: - Single story, single zone hydronic heating - Dunkirk boiler from 1992, located in basement - Cast iron radiators all on first floor It's our first house with hydronic heat, which I'm not familiar with. I understand the boiler system more or less. About a month or so ago, I noticed that the house got really hot a handful of times. We keep our standard Honeywell thermostat set at 64 degrees at night, 65 during the day. I don't remember the temp, but it was high 60's, even with the thermostat set at 64. So, I went down to the boiler and saw that it was dripping water from the pressure relief valve tubing. The pressure gauge read about 30 psi, maybe 33 tops. The temp gauge read about 190, 195 tops. Did some quick research and saw that boiler temp should be no higher than 180 and pressure should be about 20-25 when heated. So, I called a heating company and they came out, told me my aquastat relay had gone bad and was letting the boiler heat out of control. Expansion tank was supposedly fine and was verified to have 12psi in it. So, I had the aquastat relay replaced with a new one. The tech also recommended that I use a thermostat made specifically for hydronic heat, like the Honeywell Aube TH140. This is the one we currently have: [url=http://www.amazon.com/Honeywell-TH4110D1007-Programmable-Thermostat/dp/B001RZ678Q]Honeywell TH4110D1007 Programmable Thermostat - Programmable Household Thermostats - Amazon.com[/url] However, I've read that a regular thermostat like the one we have will work just fine for hydronic heating applications. Finally, tech said there was a bit of air in the system and told me to bleed the radiators, so I did but didn't get much air out. The PRV only leaks at around 30psi. A day or two passes, [B]boiler starts leaking again from PRV[/B], pressure again around 30 psi. Temperature around 180ish, maybe a bit higher but not much. The aquastat relay is set to the lowest setting (180). Called the tech back and he says my expansion tank is now bad and needs to be replaced. The reason why I'm posting this is because I have a gut feeling that the tech was either sloppy or didn't diagnose correctly. My questions: 1. Is our current thermostat okay to use with the boiler? I assumed it was fine since it appears to have been installed for a while. I mean, it's just a fancy switch, right? Or do I need one with anticipation? 2. Why is my boiler still over-pressurizing (and possibly overheating) and leaking water from PRV? Should I go ahead and replace the expansion tank? I was also told the tank is possibly undersized. I have read[URL="http://www.doityourself.com/forum/boilers-home-heating-steam-hot-water-systems/466717-pressure-relief-valve-leaking-service-your-bladder-type-expansion-tank.html"] this thread[/URL] and plan on testing the tank, but thought I would post here just in case someone might know what the problem is. Thank you to all who can help!