EKO Over Heating Problem

[Serg]

Hi All, This my first post and I'm looking for some help with an issue I'm having with my system. I have an EKO 40 with 500gal. storage that I run year round to heat our domestic hot water, and house using radiant tubing. This system has been operational since '09. About 8 months ago I noticed a change in character while the boiler was firing, in that the Boiler itself heated up faster than usual. Bear with me while I fill in some back ground. I usually begin firing the boiler when the top of the Tank gets down to 130F (bottom around 115F), once the boiler heats up and the pump comes on @143F the boiler would run up to around 170 and hold there until the return from the bottom of tank got up to around 155, then the boiler gradually run up to near 190, at the same time the top of the Tank reached 175 which is my tank controller's set point to shut the boiler down. I should mention here that I do have temp. sensors on both sides of the 3 way mixing valve on the boiler return. Once the pump kicked on the temp. on the boiler side of the mixing valve would run from 140 to 154 and stay there until the temp. at the bottom of the tank rose to near the same temp.

Yesterday, when I started firing the boiler, the top of tank was @128 and the bottom was 114, the boiler heated up as normal and the pump came on at 143. 1 hour later the boiler shut off on high limit at 195, moments later the top of the tank reached 175, while the bottom of the tank was still 119. This boiler has never heated up so quickly and with this kind of variation in temps on the tank. My guess is I have some restriction in the boiler that's slowing the flow rate but I don't know the best way proceed in proving this. Has anyone experienced anything similar to this that can share their exploits???

Thanks in advance and for your patience in this long winded explanation, but trust me when I say this is the abbreviated version.

 

[Mike Fromme]

My money is on a bad wax thermostat inside your boiler protection valve.

If it's an older danfoss it uses basically an auto thermostat that you can pick up at an auto parts store in a pinch.

Or run it without the thermostat in the valve to see if that is the source of the overheating. You'd have to close the bypass gate valve and have no return protection but you'd be able to tell if water was moving to storage pretty quickly.

 

[Serg]

Thanks for your reply Mike! I do have a Danfoss TMX valve on the bypass loop, and that is a concern, which is why I put Temp. sensors on both the Tank and Boiler sides of the valve. They indicate that the valve is working perfectly, as the sensor on the boiler side ran up to the low 150s and stayed pretty constant until the bottom of the tank caught up. Even when the Boiler controller was at 195. In the past I pulled the thermostat out of the valve and tested it in a pot off water on the stove. It would start to open around 140 and be full open at 156 so the sensors seem to be in agreement.

Any other ideas are surely welcome

 

[Fred61]

I would check to make sure the circ is actually pumping, ie, buzzzng but not turning or broken impeller. Since the top of the tank heated up that indicates some flow, perhaps from thermosyphon. Thermostat in Danfoss oriented correctly?

 

[maple1]

Circ could have also picked up some dirt or a piece of teflon or something.

 

[Mike Fromme]

Thanks for your reply Mike! I do have a Danfoss TMX valve on the bypass loop, and that is a concern, which is why I put Temp. sensors on both the Tank and Boiler sides of the valve. They indicate that the valve is working perfectly, as the sensor on the boiler side ran up to the low 150s and stayed pretty constant until the bottom of the tank caught up. Even when the Boiler controller was at 195. In the past I pulled the thermostat out of the valve and tested it in a pot off water on the stove. It would start to open around 140 and be full open at 156 so the sensors seem to be in agreement.

Any other ideas are surely welcome

I had a similar problem with my danfoss (the boiler was reaching the setpoint way too fast and not moving enough btu's to storage). The temp gauges were also showing what they should have been. But I just wasn't moving much water and the boiler would idle... The bypass valve was stuck closed but the pump was creating enough pressure to push the 'safety' spring open to prevent a complete boiler meltdown and allow some btu's to go to storage.

My first thought was a problem with the wiring or circs. After checking them I pulled the thermosat and did the boiling water thing and it seemed ok as it opened right away. I put it back and still had overheating in my boiler... I couldn't find any other restrictions or air in the system so I pulled the thermostat and ran the boiler without the bypass. Everything was fine. Thinking trapped air had been my problem I put the thermostat back one more time... And had overheating.

So long story short the pot of water test wasn't accurate for me.


I've been running a stant superstat #45356 thermostat (160 degrees it is completely open) in my danfoss tv-esbe for a year without issue. It was like $9 at advance auto. The danfoss replacement thermosat is closer to $100 . There are some differences -- the stant doesn't have as wide an opening but I haven't noticed any problems.

 

[Serg]

Guess I'll pull the pump and check it out, if it proves okay I'll pull the stant, fire things up and watch what happens. Thanks for all the great suggestions!
Stay tuned!

 

[Serg]

We'll the tests are in and Mike gets the prize for correct diagnosis. I pulled the thermostat out of the Danfoss ESBE and fired the boiler using a ball valve in the bypass loop to control the return temp. and everything worked fined. I had to baby sit the entire firing, but it was quite an eye opener. I was actually able to reduce my firing time by 30 minutes (16%), which is quite a jump in efficiency.

Unfortunately, when I installed the stant superstat #45356, as suggested, all the original problems recurred. I believe the 160 degree stat is too high temp., but was the lowest rated stat I could find at the local auto parts suppliers. According Stant (the manufacturer) their stats start to open at the rated Temp. and are fully open approximately 15-20" above that. After seeing the kind of efficiency I was able to gain, I think I could use a stat that started to open at 130 and was full open at 145. My stack Temp. runs between 350-450 so I doubt if I would get any cold sweating in the flues at 130 return water Temp.. Problem is, where do you find a stat with that rating???

 

[maple1]

Not sure about the connection between reduced firing time & increased efficiency?

And I think most of the creosote condensing ('sweating') that would happen with too low of a return temp, would happen in the firebox. Where the return water hits it.

I'd maybe look around a bit more or at more places, and see if you could get a 140 stat.

 

[Mike Fromme]

With the stant thermostat my boiler stays at 175 or so on the controller temp until the storage tanks start to warm up on the bottom. With the thermostat that originally came in the danfoss the boiler could hit its set point much sooner in the burn cycle. So in my case the stant has been working better by keeping the boiler cooler and less idling.


Depending on where you have the bypass (return or supply) a lower rated one might work better for you. The 160-180 operating range may be too high as you suggested.

Danfoss does have 3 or 4 different temp ratings. But you might find a 140 stat at a marine supply house. I know inboards like to use either 140 or 160 stats, not sure if they will be the right shape and size though.

ETA:

I don't remember exactly how the danfoss goes back together, but is it possible the thermostat can go in backwards?

 

[Serg]

There seems to be a discrepancy between thermostat manufacturers as to the meaning of the temperature rating. Stant states on their website that their Tstats begin to open at the rated Temp. and are fully open 15-20 degrees above that rating. However, when I talked with a rep at Hardin Marine he said the Tstats they sell are full open at the rated Temp. + or - 5 degrees. I was actually considering a 120 degree marine stat, but if the Hardin rep is correct then that would be too low a temp..

You can put the Tstat in the ESBE backwards, but then it wouldn't open at all since the control element would be on the tank side. I did talk to Danfoss technical support this AM and it seems my ESBE, that I purchased in 2008, is the old version and only has 113, 140, & 160 degree Tstats available at around $75 a pop. The newer ESBE's several other Temp. Tstats available.

 

[Mike Fromme]

I always believed thermostats were fully open at the design temp... Time for a stove top test again

On the tv-esbe valves I believe that if the thermostat is stuck shut (or installed backwards) that the outer spring the that thermostat mounts in will allow some flow through the valve and result in your trouble. I'm not sure it's possible to mount the thermostat in the spring backwards and fit it in the valve though.

 

[Fred61]

It's been a while since I installed my Danfoss but I think the thermostat can be installed backwards if the brass seat is installed on the wrong side. Just remember that the wax expansion element should be oriented toward the boiler and the bypass should flow over the thermostat element. The flow through the bypass is what senses the boiler temperature at the thermostat.