You didn't say what the problem was friday. As for the thermocouple, if it was the original then its was time for a new one anyway. It was nearing the end of its life. That has absolutely nothing to do though with your PRV and mixing valve issue. Seems kind of odd though that both went NG at the same time. Come to think of it, I don't think I ever had to replace a reducing valve. Had to pull them quite ofter and clean the screen but thats about it. Thats doesn't mean yours was OK but loosing both vales at the same time????????Hmmmmmm.

I don't KNOW why there was no heat Friday -- or why it came back on again Saturday.

Friday I tried setting the thermostat up above 70F -- nothing; I didn't hear the gas fire up and there was no heat. Then I set it back to the usual 68F and the room temp was still only 64F. (It only got there due to the forced air system being on in the house.) Suddenly on Saturday...heat again and heat to now.

Thanks for telling me it was appropriate for Tech #1 to replace the thermocouple. (I'm still wondering if the relacement might be faulty.)

OK, it's not working again. I see the gas is on in the boiler. The pressure says 10 lbs. The output temp is 145F. The returning water temp is 100F. There is some heat, i.e. the flooring is warm-ish, but it won't rise to meet the set temp on the thermostat.

We keep the rest of the house at 68F days and 62F nights. We leave the boiler heat on at 68F all the time. This morning the temp in the boiler-heated area was...62F (thanks to the forced air supplies in that room).

This is a north-facing room with a huge window and cathedral ceiling. It is uncomfortable without the supplementary floor heat.

So...the boiler is working, but not heating enough. Any ideas about why that would happen? Something wrong with the tubing? The thermostat? The thermostat sensor ON the boiler?

In the future require that all parts removed from your heating equipment is given to you.Make this request prior to the repaire.
Thermocouples last many years , depending on the usage and atmospheric conditions in the serounding area of the furnace.
If your furnace/ hot water heater is 7 years old then it's only operated for less than 3.5 years in reality and should have many years of life remaining on the thermolcouple. I know of thermocouples lasting 25 years ( actual operation time)
A presure Regulating Valve (PRV) is not needed at all once the system is full and has 10 to 12 pounds pressure in the system unless you have a H2o leak. You should have a bladder type expansion tank on a unit that new and the charged water in the loop shuld have been treated with a rust inhibater at commissioning. This would result in two to three years of service free operation if fired by LP or Nat Gas. Oil would require annual checks ups.
You are getting a 45 degree split through the system which should keep the floor very warm . My guess at this point is the new Mixing valve is possibly not calabrated to the thermostat. and the old one was fine and should have been left alone. Set the thermostat to the same tempeture of the room ,this should cause the hot water to bypass the floor cools and return to the hot water heater causeing the heater to cycle off. Then set the Thermostat to the highest setting this should cause the heater to turn on and the hot water split should go to the maximum temperature spread.
Next get a new Contractor.

googe -- Thanks. I've set the boiler thermostat to 68F and will wait an hour, then set it up to...oh, 72F?...and see what happens. If that brings the room up to 72F -- what does that tell me about the underlying problem?

The HVAC company will be here tomorrow afternoon.

If they want to bleed the whole system, how long should that take? I'll ask to see rust inhibitor added. The water Tech #2 drained two weeks ago when he installed the valves was very rusty.

The problem with these guys leaving the old parts is...how would I know if they were actually defective? Or if they MADE them defective?

I couldn't believe we needed two new valves or a new thermocouple after only 7 years, but I'm just this dumb housewife! I had a long conversation with the company's owner, who has been helpful in the past -- helped me choose furnaces 7 years ago when he had no profit because he wasn't our contractor's sub. But discussing this boiler mess left me feeling he was pouring syrup over my head.

Tech will arrive this afternoon to bleed the system. That's what the company manager thinks is the problem. He says no rust inhibitor is needed with this system.

I now believe that the whole problem began when the first tech serviced the boiler and added water but did NOT bleed. He also replaced a good thermocouple 'just because'. Then the mixing valve began an almost-invisible leak -- I could see moisture on a paper towel if I ran it along the head of the valve, under the cap. It seems probable that all we EVER needed was to bleed air out. Comments here convince me that we certainly didn't need a new pressure reducing valve.

After this visit, we are through with this company! Good doesn't always remain good. For all I know, the original owner isn't really running the company anymore and there's a greater push to profit.

A big Thank You for help here!

I wouldn't fret about the thermocouple, unless they charged you dearly for it. It costs less than $10 at Home Depot and is easy to install yourself.

Sounds like this contractor, or someone there, doesn't mind throwing parts (and your money) at this mystery. Hopefully the system bleed will help.

I've just found the original paperwork for when this company instlled the boiler. It was 2003, so it's only FIVE years old, not seven. I also found a PM sheet from 2005 where that tech replaced the thermocouple. (Charge is $23 for the part, BTW.)

Wednesday's bleed did NOT change anything. By Wednesday night/early Thursday morning the temp was back down to 62F, which is the forced air temp night setting. I was able to use googe's istructions of setting the thermostat down to 66F, then back up to 68F, and the boiler heat rose to 68F and stayed there last night into this morning. Now working fine -- staying at 68F. (Well, I think it is working fine; hard to say since 68F is also our normal forced air setting.)

We're enjoying a foot of snow today. I've asked HVAC company to call me when they can come out again to try again. I've suggested what googe mentioned, that the mixing valve may need to be recalibrated.

I'm at least able to 'make' this work, and it isn't our primary heat, so I'll play along and see what else this company can do as long as I'm not being charged and MORE for it. I've now nearly paid twice for this darn boiler: $900 in 2003 + $700+ now.

Chisue-
I don't think you ever mentioned if the system had cycled during the call for heat setting? The boiler may be cycling on high limit without moving water thru the system. When boiler was running are you getting flow to you radiators/baseboards. Do they feel warm? Is the pump (assuming you have a single zone) operarating correctly? Suspect loose impeller on the shaft or erroded impeller within the housing? What was the original boiler limit set at before the repairs?

keeth -- When I use the 'googe' method of dropping the thermostat to ambient room temp, then raising it to the 68F I want, it DOES circulate hot water into the tubing (and we are warm). I just did that again this morning when I woke up (and found the temp was back down to 62F again).

This is an 'add-on' system of tubing under the floors of the library and back hall (both north rooms). We had to do this to remedy the poor planning of the HVAC sub for our house; he didn't figure enough supply from the main forced air furnace for these areas.

Do I still need to think about the pump and impeller, or is this something else? Pressure stays at 10. I don't know what the original boiler limit set was, but I'll look for any old worksheets to see if I can find that.

Thanks to all here for trying to help. I feel a little better knowing there are some 'good guys' to counter the run-around I've been getting from our formerly-trusted co.

The question I need to now is- if you set the thermostat to 80 and let it run would it shut down before reaching setting? Does it simply quit or does it continuely run but the room does not seem to heat? You appear to confuse the imtermittent operation of the boiler with the ability of it to heat the space. Both are different symptoms. Be specific please.

keeth -- The tech said the underfloor heat would *never* heat the library to 75F. (This is where the thermostat is located.)

Up until this autumn we have always set the boiler thermostat to 68F in the fall and the room stayed at 68F until we set the thermostat down in the spring. I've used the room nights when I was unable to sleep. It's been a consistent 68F day and night.

The problem now is that sometime in the night the underfloor heating stops heating to 68F. I think it stops circulating warm water altogether and the library's only heat source is the furnace. The floor doesn't feel ice cold, but barely warm, and not toasty (as it does at 68F).

This morning is typical of the problem. The temperature in the library was the same 62F as the rest of the house. (We set the forced air thermostats down to 62F at night.) This morning I dipped the boiler thermostat from 68F to below 62F; waited 20 minutes; set it back up to 68F. The floor began to warm and the library quickly reached 68F and has stayed there all day.

Personally I'd start by shopping around for a repair service that is honest and competent.

seattlepioneer -- We ARE doing looking for a new HVAC company. One of the ways I hope to determine who IS honest and competent is by trying to find out here what's really the problem with our boiler system.

keeth -- I found an old tech worksheet. The boiler had been set to 170F. Now it's at 145F. Could that be why it shuts down at night? How do you change the temp setting?

BUMP!

This is still not resolved.

A tech came and said he had set the mixing valve to 170F. He left and that night the system failed to keep the room temp up at 78F. It fell to the 62F along with the rest of the house.

Next tech came. Said the mixing valve has a 150F limit, but that that should be adequate. He tested the entire electrical hookup and said...the thermostat needs to be replaced.

I refused their on-truck non-programable thermostat at $104 and have bought a Honeywell the same size and style as the existing -- a T87F for $25. I will install this.

QUESTION: If the thermostat was the problem all along...why the heck am I paying $700 for new valves!!!

I haven't paid the charges on my charge card yet. Do I have basis for complaint? The company has not charged for the last four visits...but they also didn't FIX the problem. I don't even know yet if the new thermostat will fix it. Should I call the CC company and make a complaint?