Hi all, I'm new to the forum...
I've a P368V water boiler with tankless domestic hot water. At the mixing valve, the "hot" pipe measures around 160F and the "mixed" pipe about 95F, with the knob turned all the way to hot. Does this little info clearly point to a bad mixing valve? I would think (and hope) that if the knob setting on the valve is turned all the way to "hottest" you would get nearly the same temp out as the input temp. The baseboard heat seems fine. Are there many things to consider when replacing this valve other than the 1/2" sweat fittings at all 3 connections?

 

Maybe I should rephrase my question?

How do you go about checking the mixing valve (tempering valve?) for the hot water (for the shower, taps, dishwasher etc.) on an oil fired water boiler?

This valve has a knob with 3 pipes connected to it labeled; hot, cold, & mixed. There is no electrical wiring at this valve. The knob is labeled "hotter and colder". The problem is the hot water is not hot enough at any tap etc. On the surface of the "hot" and "mixed" pipes at this valve, I read 160F and 95F respectively, even with the knob turned to the hottest, with a surface thermometer.

 

It certainly sounds like the tempering valve has gone bad. Depending on brand, on some replacing the guts is pretty easy.

 

Sounds like your mixer is failing, but I'm not very experienced here. I just replaced my mixer valve because it was leaking and also because it was due for a new cartridge (it was an older Taco mixer), my hot water temp went from barely warm enough for a shower on the old Mixer, to totally erratic with the new Taco mixer (temps ranging from nearly scalding hot to almost as cold as my cold line). My boiler is doing ok, but I'm not using a thermometer to measure pipe temps, so my problem is probably different and probably needs its own discussion.

 

Thanks guys...I didn't think the valve itself might be repairable. I'll look into the brand and model.

 

Well the mixing valve is indeed the problem, seems it failed in the "most cold" position. After disassembling and cleaning out the crud, I found that by removing the adjustment knob (which incorporates a stop) I was able to adjust it further warmer, getting me into the acceptable hot water realm at no cost. It may be that this device is no longer making any active adjustment to the temp, but it still seems to always be well below the dangerous output temp. I was unable to find a repair part for it, so I may live with it like this a bit longer.

 

In the meantime, I would instruct any household members to be aware that it's 'possible' for extremely hot water to be discharged... particulary the elderly and the young!

I would replace it sooner than later... but if yer careful and can live with it until weather warms, you should be OK ...

 

Thats the way I saw it NJ Trooper, thanks

 

Similar situation here, over the years. Weil McLane P66HEWT, domestic coil (excuse me... "Tankless hot water coil"), 2 different flow reducers and a Taco mixer valve. My mixer was a tiny little bronze thingy with a bent black metal knob.

Unscrew the knob screw, turn the stem hotter and tighten the knob screw, sound familiar, yes? lol! Been there, done that, rebuilt that one twice with a new cartridge (which fixed the problem of water temperature drifting towards cold after a minute of normal mix). Eventually the valve stem seal failed (was dribbling water all over the case of the furnace), so I had to replace it with a newer, BIGGER, more expensive Taco with a green cap on top.

What is it with NH using Weil McLane boilers and Taco supporting parts? Must be the local suppliers. Beer 4U2

 

Tankless is the least efficient way to make hot water.

Best is an indirect tank, but you can for cheaper use a simple electric tank to mix and hold hot water. The tank thermostat controls the water temp. It starts a pump pulling cold from the bottom the tank through the tankless coil.

With tankless coil the boiler fires every time you use a little water. The mixing/storage tank should have the cold fed to it and not the tankless first or you have the same inefficient and unnecessary firing of the boiler.