Strange problem with mixing valve

[Mike T]

Hey Guys-

I had a weird thing happen with my boiler yesterday. The wife noted the home was getting much cooler and saw no heat was coming out of the PSU unit in a bedroom.
I walked her through the basic electrical and switch checks and confirmed with her the boiler was up to temperature.

So... the plumber came out. He determined that there was no water circulating betwen the boiler and the rest of the plumbing, but the circulator appeared to be working.
He believes the mixing valve was stuck closed and not allowing water to circulate. A couple hard raps on the mixing valve housing appeared to free it up and its working fine again.

I have the Danfoss mixing valve that New Horizon sells. I haven't heard of the mixing valves doing this before and wondered if anyone else has.

FWIW- I thought the circulator would have been the problem, but the plumber saays no. He says circulators work or die- he hasn't had an intermittent one.

 

[stee6043]

This wasn't one of your first fires, was it? My Danfoss valve came from the factory "backwards" and I had to swap the element around. I wasn't the first to have this problem. But if you have had good heat output in the past and this is the first issue I don't think it'll be that type of problem.

Did you treat the water in your boiler when you filled it? How old is the valve? I've never heard of someone on this site having a clogged Danfoss but I can tell you from experience that this type of thermostat will wear and they do fail. Ask any auto mechanic. In fact, I have one stuck open on my truck right now.....just too lazy to fix it yet....

 

[Mike T]

The boiler has been running since November on a two year old system.

It has the same water mix that the regular burner uses.

 

[WRVERMONT]

Glad to hear system is running again. Just curious, do you have the "balancing valve" installed on the bypass line from the supply?
Happy New Year!

 

[Mike T]

Glad to hear system is running again. Just curious, do you have the "balancing valve" installed on the bypass line from the supply?
Happy New Year!

I am not the plumber so you have to tell me what the balancing valve is. FWIW- the mixing valve has two lines coming in-
one from the system and one split off from the boiler output. If I remmeber correctly the one coming in from the piping system is on the bottom.

 

[WRVERMONT]

The line split off from the boiler output is the line I am refering too. Usually a ball valve is mounted between the boiler supply and the Danfoss valve.
If there is no valve this could be problematic.

 

[Mike T]

There is a shut off valve on that line with the handle- I assume that is the ball valve

 

[WRVERMONT]

Is the ball valve partially closed or wide open? The purpose of this valve is to balance the flow from the boiler supply and the system return. When balanced the Thermic valve(Danfoss Valve) can then just "look" at water temperature and do it's job properly.

 

[ManiacPD]

I think I had the same valve, mine was an ESBE 60C/140F, 3-way thermic valve. If so I took mine out.

On initial startup my storage water was 55F and after burning for 12 hours I had 90F water in the storage tank. It was all going through the bypass and recirculating to the boiler. Then I was about to overtemp the boiler. For my setup I determined that valve was useless and took it out. Until the return water hit 140F it wasn't going to let hardly any water out of the tank and into the boiler. I wasn't about to fire it all night in hopes of making that happen.

Also noteworthy was that we initially installed it backwards and nearly blew the system up. I had lots and lots of steam and no place to put it. When the valve finally opened the hot steam traveled through the boiler return and into the dip tube of my tank. 260F steam hitting 55F water makes scary noises.

I think if I had a cast iron boiler and I needed to thermally protect it I'd work with this thing but for now it is gone and the system works perfectly.

Good luck!

 

[in hot water]

tight tolerances inside those valves dictate they be disassembled and cleaned from time to time, even in closed loop systems. It's a good idea to install them with isolation valves on all sides to ease the disassembly for cleaning.

Ocassionally the wax cartridge inside them fail, generally they fail "cold" when that happens.

hr

 

[Mike T]

I called Zenon at New Horizons. He said the thermostat went, but that all I need is the part not the whole unit.
$35 plus shipping sounds a lot better tnan a couple hundred!

 

[Mike T]

Ok- Installed the new thermostat and fired her up. Appeared to be working great and then .... the return stops flowing.
To test it I pulled out the entire thermostat assembly and rreinsatled the cover of the mixing valve without a thermostat.

It works. Any ideas?

 

[Gooserider]

Possible you got a defective part that "died young" on you... How is the tolerance on the parts? Any sign of corrosion or other crud that might be jamming it? I'd say call Zenon again and see what he has to suggest...

Gooserider

 

[chuck172]

Don't know about the Danfoss valves, but the termovars have built in isolation ball valves.

 

[Mike T]

There is nothing at all I could locate for crud or corrosion.

I sat down and looked at the system again from a piping viewpoint.

If I assume the thermostat is actually working correctly, I can then assume that the return leg gets too cold to allow the thermostat to open. With the colder weather (and a new install this season) I am wondering if that could be the cause as the heat is being used in the zones, and the return doesn't get hot enough tom open. There was no probem with warmer temperatures, but it did get colder.

Havng said that, I have the mixing valve located behind the boiler. The supply and return lines join into the system about 15 feet away, but the supply must go through all the piping before it hits the return. This system is hooked up in what I believe would be referred to as a series ( it goes into the regular furnace supply and return so that if there is a demand and the temperature drops enough the furnace kicks on ( Biomax out of fuel).

Should I have the plumber install a leg from the Biomax supply further down the system to "heat" up the return? Maybe install a one way valve to isolate the plumbing to the propane furnace? Move the mixing valve all the way down to where the systems join?

I don't want to install a lower temperature mixer as I don't think it would be a good idea.

 

[Mike T]

Just read a similar post...would a balancing valve installed at the beginning of the return solve this?

I also noted that the hot water on the loop from the boiler supply that goes into the three way valve does not have any mix at all with the return water until it goes inside the Danfoss. Should this have a split form the return water so the valve actually mixes the boiler water and return supply in this line?

I think this would work on getting a mixture of hot and cold water into the sytem but await an expert's opinion.