T87F anticipator appears faulty

pacoit

I have a 2-pipe vapor steam system. I've kept the anticipator on the T87F all the way to the left (longest cycle) for many years, basically off. When I try to move it even only a fraction of a mm to the right, I get a super short cycle, ~4 min.

I've tried to clean it. Removed from wall and sprayed electronic cleaner on it, swabbed it. Nothing changed. It is perfectly level on the wall. Any ideas on how to fix it or diagnose it further? Thanks.

pecmsg

how does it cycle on max?

Big Ed_4

What is the reason why you adjusted the anticipator ?..

pacoit

The temperature overshoots quite a bit. So there are very long cycles of an hour or more, and large temperature swings (say, roughly 4F).

When I got a new boiler in 1997, the techs repositioned the anticipator (maybe 0.8); it short-cycled (~5 min on); called them back; they said everything was set right (obviously not). Shortly after, I found the little anticipator lever, pushed it left until it cycled as before. Only in the last month did I discover that it is just a variable capacitor that goes on and off with the tstat switch; left=high resistance/less heat; right=low resistance/more heat. I figure dirt or something may have created a short. No luck by cleaning. It's hard to examine it visually, made as it is. Any ideas to fix or diagnose further?

mattmia2

it is a power resistor in series with the heating circuit. if the tab or the surface is dirty it won't make good contact and I think the entire resistor will be in series and it will be at the longest cycle setting. try rubbing it with something like a business card with alcohol on it or try a couple drops of red deoxit. you can measure it with an ohmmeter.

EBEBRATT-Ed

Change the thermostat. On the older thermostats like the T87 you are supposed to measure the amps flowing through the thermostat and set the anticipator to that amp setting. I found that this did not work sometimes and you would get short cycling (close temp control) or long cycles (wide swings in temp) so usually you just play with the adjustment to get what you want.

T87s are long gone unless you can find one on E-Bay. Honeywell makes an electronic round model and of course there are other electronic stats.

I doubt you will have any luck fixing yours.

HydronicMike

Are you sure it’s not short cycling on pressure?

pacoit

@mattmia2 , I can try cleaning it some more. I put an ohm meter to it; the value jumps around a lot (not sure why). I'll try that again, too.

@EBEBRATT-Ed , I tried several position; all fast.

@HydronicMike , Short cycling on pressure? Hmm, I don't think my vapor system has ever experienced such a phenomenon…I think the pressuretrol is still a virgin…the 100 year virgin. I haven't seen more than 2-3"H2o on the 0-30 gauge, so, < 0.1psi.

mattmia2

make sure the pivot end of the wiper for the pot is clean too

109A_5

I expect the resistance is quite low, an inexpensive meter may not do a very god job measuring the resistance. I also expect the wiper part of the circuit may have a poor connection, so you get the whole resistor (maximum anticipation, maximum resistance, maximum resistor heating) or where you had it originally, no resistance (no anticipation).

https://inspectapedia.com/heat/Heat-Anticipator-Ohms-Law.php

Some information here, although I think they got this part wrong.

https://inspectapedia.com/heat/Heat-Anticipator-Ohms-Law.php

EBEBRATT-Ed

@pacoit

Bunch of T87s on E-Bay in the $30-$40 range.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1870821#Comment_1870821

that seems like a lot to take the mercury off your hands…

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1870827#Comment_1870827

Don't stick your hands in the mercury. That stuff can kill you.

pacoit

Update: I took the T87F to the workbench; removed the plastic dial for clear access to the anticipator; I used electronics cleaner, alcohol, qtips, and compressed air. A resistance test gave a range of ~1-7 ohms, right-to-left, smoothly increasing. However, when I re-attached and tested the anticipator, it did as before; it cycled off much too quickly, ~5 min.

By the way, if it helps to know, the amp reading of the tstat wire at the boiler is 4.8A.

Jamie Hall

If the boiler control is drawing 4.8 amps through the thermostat…. something is odd. Ind of surprising the transformer can even supply that. The anticipator range is 0.1 to 1.3 amps, so naturally if you are pushing 4.8 amps through it it won't cope at all.

But I'm puzzled by that amp draw — most modern controls are down at the 0.1 amp range?

mattmia2

what control or gas valve or primary control is it controlling at the boiler?

EBEBRATT-Ed

Can't be 4.8 amps. You would need a 115va transformer to support that.

pacoit

1000 pardons! The amp reading is 0.48A.

Jamie Hall

Try thoroughly cleaning the anticipator slider and resistance coil. Do NOT use any abrasive! I use DeOxit for that kind of thing, but there are other contact cleaners that work too. Spray it on the coil, then run the sider back and forth and back and forth until you get bored…

0.48 amps is a little more reasonable. After you get things cleaned up a bit, start with the anticipator set just abut in the middle.

109A_5

" A resistance test gave a range of ~1-7 ohms, right-to-left, smoothly increasing. "

It seems maybe the resistor is connected backwards, although not sure how. To the left should be the lower resistance to the right the higher resistance. The goal is to produces a relativity small but consistent amount of heat for the anticipation function regardless of the needed primary control load current (different systems have different equipment).

So if you have a 0.8 amp primary control load you need less resistance (to the left) than if you have a 0.15 Amp primary control load, with the 0.15 you would need more resistance to generate the same amount of heat.

Since the primary control load is the predominant factor determining the load current, varying the anticipatior's resistance will slightly change the amount of heat generated. That's why moving the setting to the left is less resistance, less heat, longer system run time.

mattmia2

if it gets a higher voltage to the t-stat it can burn out the pot, make sure you have continuity between both ends.

pacoit

I thought a higher resistance generates less heat. The highest resistance, e.g., a cut wire would generate no heat. All else being equal, the longer the wire the more the resistance, so less current, and so less heat.

My understanding is that the anticipator is just a variable resistor; when the copper lever with a pin contact that touches winding is moved along the winding, it shorts the wire where it is positioned. If moved left, the wire length (and resistance) increases; to the right, it decreases.

My primary control states 0.8A.

Jamie Hall

Ah. But a flaw — a minor one — in your logic. The current through the anticipator is not set by the anticipator — it is determined by the device being controlled. The actual resistance of the anticipator affects the current flow only slightly. So… the longer the path through the anticipator element, the greater the heat being generatred — and the quicker the anticipation.

Here is a good article on them…

Thermostat Heat Anticipator Resistance Ohms Law