Mixing valve/domestic coil

STEVEusaPA

Hello wallies, have a problem, trying to diagnose.
I have a customer (landlord) with a rental. Oil fired boiler, with a coil. The complaint is no domestic hot water. Here's what transpired.
Last week tennant called, said boiler making strange sound. Had her go over and check the temp gauge-220 degrees! Told her to shut it off, I'm coming over. I found the triple aquastat wouldnt shut off burner on high limit (had to turn down hi limit to 140 to have it shut off at 200). So I replaced the aquastat.
The next day, tennant calls and says no hot water. She said they are working on the soil pipe and had to shut the water off. When they turned it back on, no hot water. Had her feel the domestic pipes, all 3 cold (cold, hot, mix), but has pressure and flow at the fixture. I called the landlord and said the mixing valve was probably destroyed by the boiler maintaining too hot a temperature (dont know how long). Landlord said he has a plumber who will change the mixing valve. Plumber calls me tonight and says he cant get hot water out of the boiler-all 3 domestic pipes cold. I surmised the coil is blocked, probably from the first plumber, or the filters/screens are blocked/plugged in the mixing valve, and the cold water is bypassing the plugged coil and going into the mix. He claims its not possible because he would have no flow. I think if the coil were plugged, the mixing valve would work just like a failed mixing valve-all cold water.
What do you guys think.
Thanks
Steve

Snowmelt

Is the boiler hot when your trying to get domestic water. There might be so much scale on the tankless coil that it's not getting hot although it should be warm. Did they install a triple aquastat in the boiler.
Can you pull the coil out and soak it in flow-aid or simple green?

STEVEusaPA

Thanks snowmelt. Oh yes, its up to temperature. What are your thoughts on the coil being plugged and the incoming cold is just flowing thru the mixing valve?
Yeah, all domestic pipes around the mixer ice cold.

hot_rod

does the mixers have union connections? Pull it out and see if there is flow thru the coil. if so the valve could be stuck from debris that was dis-lodged during the work.

Easy to dis-assemble and clean a TMV, keep an eye on the spring and order of parts.

Mixers installed on high temperature coils like that will need routine cleaning, maybe even very 6 months if you have hard water.

Soak the parts in vinegar unless it is completely plugged shut.

icesailor

In my experience, there are few mixers available now. But they most all had the cold water entering the bottom and the hot entering one side near the top and the mixed hot slightly above the hot on the opposite side. The valve will not work without the element "Guts" inside, nor will it work if the thermostatic element has burned out. They burn out from excessive heat. #1: Is the valve "heat trapped"? #2: Was the element assembly removed before soldering like the instructions tell you? Because if you do not, the heat of soldering will ruin the thermostatic element.

Even if the coil is seriously limed up, you still get a burst of hot water for some short period when you first turn it on.

If the water is really "Limey", that excessively hot water will accelerate the accumulation of lime deposits in the coil. What kind of boiler is it? Are there a lot of white fuzzies where the adapters go into the coil? The plumber should know this. If the water is conductive, and de-zincification is going on (told by brown sections of bronze/brass) and washer heads are falling off, there could be a faucet washer screw head in the inlet of the coil or the mixer.

My cash first goes to a burned up element from overheating the mixer when soldering. Get a new mixer of that same type and manufacturer and swap out the inside "guts" only. If it works, there's your problem.

But, when you stick your finger right where the adapter comes out of the hot side of the coil, is it at all warm?

Install a ball valve on the cold going into the valve, after the cold water inlet to the coil. Shut the valve off. If you get hot water through the valve, the element is bad. I've never replaced just the element and had it work. Only the whole assembly for the valve. We/I always did that on tankless's with mixers in case the element got bad or the coil was liming up.

STEVEusaPA

Thanks both for the responses.
@hot rod...the landlords plumber went back after the other work was done, and replaced the mixing valve. He and the landlord keep saying its something wrong with the control I put on, even though the boiler is up to temperature and working fine. They don't want to pay me to do any domestic plumbing. It's only hot/warm right at the outlet of the coil--even with flow thru a fixture.
@ice...to answer your #2, no soldering issues, the plumber used a pro press, because none of the shut off valves work completely. And because it's for the landlord, he wasn't getting paid to shut the water off and replace or add any. (He could've used pro press shut off valves. And to answer your #1, no heat trap on the new.
The landlord wants me to go back and 'take a look'. I said: Why? and "Can I cut the valve out, put on shut-offs, check for flow thru the coil and put in new mixing valve (or take apart the latest 'new' valve and clean it) piped properly?" He says, "I can have the plumber do that".

My main thought was if the coil is plugged, will water just flow thru the valve, by passing the boiler completely? That's what I think is happening, if it's possible.
Thanks again for your responses.

hot_rod

is it a three way thermostatic mix valve or one of those "extender" types. Got a pic or a drawing of how it is piped.

STEVEusaPA

Thanks Hot Rod. If I go back I'll take a pic...of course if I go back it's only to make it right

icesailor

I was unaware that they made a mixer you could ProPress without soldering it to the body.

If YOU are a HEATER, why is a plumbing problem your problem.

STEVEusaPA

I'll double check that, if I have to go back (probably to change the control because they put in an electric hot water heater).
Maybe he soldered to the body and Pro Press-ed (sp) it to the boiler and other piping--good point.
It's the only landlord I'll work for-about a dozen properties. And usually there's never a problem. Just trying to help, and like I said earlier, landlord and plumber thought it was the boiler control.
Thanks for the reply's

JeffM

There are ProPress tailpieces available that can be joined to the union threads of some mixing valves (no soldering). I don't think that's offered as a complete kit, but a clever installer can put it together.

hot_rod

Yes you can buy press tailpiece kits. Caleffi offers 3/4" press tailpiece/ nut kits that will fit any 1" G thread (BSP)

Viega also has a selection, perhaps others?

icesailor

It doesn't matter what or how you connect it.

My point was that you are supposed to take ALL of the guts out of the valve before you solder it. Every freaking one. Its in the Instruction/Installation manual.

In my experience, the description of how the valve was reacting after the change, was usually indicative of someone soldering the valve without taking the guts out.

When I installed Taco 57* valves, I always took the actuators out so I didn't have to heat the excess metal. With the higher temperatures of lead free solders, its really easy to overheat fittings. Especially Ball Valves. Where if you close the valve or leave it half open, you distort the Teflon seat and it leaks.