Thermostatic Valve- what is the purpose?

[Bob Lentz]

I know how it technically works. Just curious as to why it's needed?
I ask because my plumber didn't install it and i will have him come up and install it this spring. I know CB says if it's not installed, it will void the warranty.

[brokentoe]

The purpose is to keep the water above 150.  At 150, the valve still allows some through the building but the majority is diverted back to the wood furnace.  My dealer said that when a furnace gets below 150 there is a chance for condensation in the firebox and if that continues, over periods of time, it can have a tendency to be tough on the firebox.

[mrwood]

That is what cb says, that it will void your warrenty but I have never come across a CB in the area that uses one. Even my dealer said take it off. I am thinking of removing mine during summer shutdown. 

[Bob Lentz]

The only time my water goes below 150 is if the fire is out and the thermostatic valve ain't gonna help that situation
In fact, the last two times i lost the fire, the water never went below160 before i got it fired back up.

Seems like another moving part that in time will fail, just like a car thermostat.

[boilerman101]

I believe they use it to eliminate "shocking" the boiler with cold return water. CB says when you return water below 150 the firebox sidewalls will condensate creating acidic wet creosote potentially causing a corrosion problem. I think they just started including it with both their Classic and Eclassic boilers in the last couple of years and requiring it for warranty. I can see where it could really help on heavy heatloads, or users that allow their boilers to run out of wood frequently allowing temps to drop. I have one installed while I also keep my boiler up to temperature so it does not affect my operation, but worth it to me not to void my warranty. My Eclassic was a big investment and worth it to me to potentially extend its life and not void warranty.

[Bob Lentz]

i don't see how the thermostatic valve will prevent cool return water if the boiler fire goes out for an extended period of time. If that is the case, all the valve is doing is preventing the already cool water from hitting your heat exchanger.  I guess what they want it to do is try and preserve as much heat in the water by not going to the exchanager. That kind of makes sense. I wonder how long the water would stay above 150 if there was no heat load?

[Holmes]

  If you let your heating system inside the house cool down to 60* then turned the heat on the water in the pipes would be 60* going to the heat exchanger. This in theory can send 60* water back to you OWB. The mixing valve prevents that from happening.  Although all of this is not  likely to happen do you want to give them an excuse to not warranty  the boiler?

[Roger2561]

I know how it technically works. Just curious as to why it's needed?
I ask because my plumber didn't install it and i will have him come up and install it this spring. I know CB says if it's not installed, it will void the warranty.

Hi all, Because my OWB is plumbed through my oil furnace, it acts like an early warning system for me.  If I hear my oil furnace kick on, for some reason the water temp in my E-classic 1400 has dropped below 165.  The water temp never has gone below 177.  When the water hits 177, it's because all 3 heat zones are asking for hot water at the sametime putting a bit of a load on the OWB.  There generally are a couple reasons for the water temp to drop to 165; 1)  The fire has nearly gone out.  2)  The is out.  As a warning system, when I hear the oil furnace kick on, I investigate for the reason (I don't want that thing running anymore than necessary).  One time the fire was completely out (my fault).  The time the fire was nearly out but I caught it early enough (running oil furnace woke me) that just a few pieces of kindling got it going in matter of minutes and water temp climbing.  So, I'm rather happy with the way my OWB works in concert with the oil furnace as an early warning system.  Plus, I shelled out quite a bit of money for it and I don't want to give CB any reasons for not covering their warranty.  Roger

[doctorb]

I do not have the thermostatic valve in my system, mainly becasue I installed 1 1/4" pex and the valve they sent me was for 1" pex.  I have the same set-up as the valve, but without the thermostatic control.  I have a loop in my basement that returns the water to the stove without going through the heat exchangers. I just have to open / close some valves and I'm done. I use this when I am on vacation, or any other time the stove will be out for a period of time (just like this winter with my short-lived back problem).  As my stove has never, ever had a temperature below 170 when I am home, I don't think that the valve will help me at all.  I understand the reasons for it, but those conditions (temps less than 150 degrees) have simply not developed as an emergency with my system.  These OWB's require some daily attention, so you are going to know when the temp is falling out of the expected usual range, and the temp drops when the fire is burning less efficiently are not precipitous.  I really like the idea of doing this manually.  I must be a control freak! :D

[buckgrunt]

I like having the thermostatic valve due to the fact that there have been several weekends during the winter when we leave for the kids sporting events (hockey tournaments and swim meets).  This results in the fire going out in the OWB and the water temp falling. When the water temp in the OWB gets below 150, the valve diverts the flowing water back to the OWB rather than to the plate heat exchanger.  This prevents my oil furnace having to work harder to heat up all the water in in the OWB. 

Dr B:  I also have 1 1/4 inch pex lines and my dealer actually provided me with a thermostatic valve that accomodated this larger size. I had to pay an extra $35 bucks for it, but it was well worth it....

[Logging logginglogging]

You should be able to find reducers to install 1 1/4 pex any way on that valve.
I am thinking of installing mine... Has anyone actually seen condensation on the inside of the firebox? and has anyone ever seen one of these newer central boilers ever rot out and leak?

[beenthere]

Being "newer" and "rotting out" likely won't happen, as too early to tell.  ;)

But water will rust a boiler if there is still oxygen in the water that will de-gas when the temp fluctuates. Water that has been heated and then cooled will not degas with just fluctuating lower temps (like when idle and no fire). Its why any new water added to my boiler system is raised to 180 deg temp before letting the system cool down.

[sparky1]

logging, you wouldnt want to put reducers on the valve. Im sure docb rand 1 1/4 for the volume, reducing it would defeat the purpose of running 1 1/4. 

I installed mine like many others, because of the waranty. Thats the only reason. If my OWB takes a crap and they wont cover it due to me not putting it in id be pretty upset with myself. Like everyone on here were running our OWBs to stop payin the oil companies, so Id assume everyone is keeping up with filling their furnaces.  Id just install it and be safe.

My dealer too said it wasnt a big deal to put it in. He also didnt have to fork out over 8 grand for the furnace!!

[747mopar]

I know this is an old thread but I just took delivery of my new 750 Edge HD and am wondering the same thing. My Central Boiler dealer told me to not use it, he says with the new HD model being stainless it isn't needed and that they're problematic? In my case I have another interesting point, I purchased one of the new Taco VT 2218 pumps which can monitor the return water temp and adjust the water flow accordingly so wouldn't that solve the problem?

[Gary_C]

First a disclaimer. I do not have one of these valves on my CB as I bought it just before they started requiring one and am not certain of what type of valve is provided. But I am very familiar with boilers and hot water heating systems and do know the reason for this bypass valve. 

Pretty sure the valve is actually like a mechanical mixing valve that is set to a 30 degree differential. What it does is prevent the water temperature differential between the hot side and return side from exceeding 30 degrees. The reason for trying to maintain a differential of less than 30 degrees is to prevent cold shock on the walls of the boiler which could crack the steel. It does not necessarily try to maintain 150 degrees in the return side. The 150 is only relevant because the normal hot side setting is 180 degrees.

As to your question, it's hard to say for sure if your pump could substitute for the valve. It all depends on the heat exchanger loads and how much you could affect return water temperature by increasing flow thru the system. Since stainless is more prone to cracking, do you really want to risk your boiler on the chance the pump could protect it?

I'm not sure why the installers are so biased against the valve, other than its a pain to install, but it seems like good insurance to me.

[thecfarm]

Boy,those CB engineers think alot. I don't have one on my Heatmor and it was installed by the dealer installer. Does sound like a good idea,but the warranty thing has me thinking. But I suppose like the insurance company,don't install a wood stove according to firecode and something happens,they can just walk away.

[747mopar]

First a disclaimer. I do not have one of these valves on my CB as I bought it just before they started requiring one and am not certain of what type of valve is provided. But I am very familiar with boilers and hot water heating systems and do know the reason for this bypass valve.

Pretty sure the valve is actually like a mechanical mixing valve that is set to a 30 degree differential. What it does is prevent the water temperature differential between the hot side and return side from exceeding 30 degrees. The reason for trying to maintain a differential of less than 30 degrees is to prevent cold shock on the walls of the boiler which could crack the steel. It does not necessarily try to maintain 150 degrees in the return side. The 150 is only relevant because the normal hot side setting is 180 degrees.

As to your question, it's hard to say for sure if your pump could substitute for the valve. It all depends on the heat exchanger loads and how much you could affect return water temperature by increasing flow thru the system. Since stainless is more prone to cracking, do you really want to risk your boiler on the chance the pump could protect it?

I'm not sure why the installers are so biased against the valve, other than its a pain to install, but it seems like good insurance to me.

The reason they don't like them is that they're prone to trapping air (so they say) and can be a pain. I'll just go ahead and install it, I want every precaution taken to protect my investment. I may also be at another great advantage to others regarding purging air, my boiler is considerably higher in elevation and I took care to dig deep enough my piping is all well below the boiler.

[Logging logginglogging]

logging, you wouldnt want to put reducers on the valve. Im sure docb rand 1 1/4 for the volume, reducing it would defeat the purpose of running 1 1/4.  

I installed mine like many others, because of the waranty. Thats the only reason. If my OWB takes a crap and they wont cover it due to me not putting it in id be pretty upset with myself. Like everyone on here were running our OWBs to stop payin the oil companies, so Id assume everyone is keeping up with filling their furnaces.  Id just install it and be safe.

My dealer too said it wasnt a big deal to put it in. He also didnt have to fork out over 8 grand for the furnace!!

the slight reduction would not be noticeable at all. the valves have a very large internal volume as well.

[E Yoder]

I know this is an old thread but I just took delivery of my new 750 Edge HD and am wondering the same thing. My Central Boiler dealer told me to not use it, he says with the new HD model being stainless it isn't needed and that they're problematic? In my case I have another interesting point, I purchased one of the new Taco VT 2218 pumps which can monitor the return water temp and adjust the water flow accordingly so wouldn't that solve the problem?

The Delta T pump could help as it will ramp up during a load, move more water and raise the return water temp. But what it can compensate for all depends on the heat load and piping size.
The cooler return water theoretically could cause sweating on a spot where it impacts the water jacket. With stainless that shouldn't be an issue as far as corrosion but (possibly) could still be a stress issue. And I think (and I may be wrong) that the outer water jacket is still mild steel? So that might be a reason to keep the valve.
On most systems the return water temp stays above 150 anyway and it isn't an issue. I guess CB wants to be sure. I personally have never used one but haven't installed CB either.

[Gary_C]

I'm not sure where this idea of condensation, sweating or corrosion comes from but I sure don't see it as a problem around the return side. We are talking the outside of the heat exchanger that is exposed to the air or more likely insulated and return temperatures of anywhere close to 150 degrees are no where near atmospheric dew points. Sure, if you were filling the boiler with 40 degree cold water you could have some issues on the pipe but not near the insulated wall of the boiler itself.

[E Yoder]

I think it's more about the steam in the smoke/exhaust condensing if it contacts cooler metal. I think I said water jacket and I should have said firebox/flue.

[Gary_C]

It would take a massive amount of cold water to enter on the outside of the water jacket, not mix with the high temperature water in the water jacket and then overwhelm the firebox temperatures of 1000 degrees plus and then cool a spot on the firebox wall to below the firebox dew point.

It's just not in the realm of possibilities and like I said, I don't know where the idea comes from. 

[superwd6]

The manufacturers instruction CLEARLY state how to install the valve and exactly what it does. Central boiler designed that part for everything that's wrong with the heating industry. That being nobody reads the manual, including many licensed heating contractors. Many Kerr oil boilers  plugged, and rotted chimneys and boiler heat exchanges from poor plumbing practice .manual Clearly stated MINIMUM return temp 140f. Low water return temp from large capacity cast iron rads killed many from condensation. Now think about the wood boiler industry,no offence please but many are installed ,sold and serviced by people with 0 license and very little heating experience .then ran by people that think they know better 🤨. I never installed my valve either but I recognized how hard Central Boiler was trying at that time to solve issues. My suggestion  is read many opinions before you follow an internet "experts" advice 😂