Slantfin VHS-150 EP Aquastat

gcubed · October 24

hi all, been trying to search through the forums and did some troubleshooting myself but hit my limit.

Recently moved into a house that has a slantfin LP boiler with an L8148E aquastat. The zones are all controlled by a Taco SR506. Has 6 zones, 3 radiant floor heat, 2 HW baseboards and 1 indirect HWH.

The issue i have noticed is that all summer (since i moved in) the boiler would fire without a call to it. Would catch it running without lights on the Taco. Reading through here, with the aquastat this should be cold start and should only run when it’s called for. Called the company who serviced it prior and they were more than useless (was told yeah, that’s just how it is, it’s not cold start). I decided to poke around and see why it was running without a call and checking over the wiring, everything looks right from the taco to the T/TV terminals.

What i did notice was that the terminals on the aquastat have continuity all the time. I took the wires out of zone controller and those 2 terminals were open. Tested the wire coming from the Honeywell and sure enough it was closed. Pulled the wires from the aquastat and the terminals themselves are closed. I can’t see any jumpers there, so no idea why it’s closed. Is it possible the aquastat went bad at some point? Is there something im missing or do i need a new aquastat?

Unfortunately I don’t stop have contact with the old owners to see if it was always running warm start… i added heat pumps and besides winter it’s only supplying heat to hot water, and the low diff that is hard set on the Honeywell has it eating through propane for no reason 9 months of the year.

mattmia2 · October 24

If you disconnect the wires form t-t on the honewell aquastat, does it still fire? the place to test for continuity would be on the wires you disconnected between t-t.

t-t on the honeywell aquastat/relay will have continuity because they are connected to the transformer and the coil of the relay.

Big Ed_4 · October 25

The boiler also has to start up to produce hot water, what aquastat control is used on the hot water tank ?

HVACNUT · October 25

The wires from T/TV on the aquastat should go to XX on the zone panel.

What do you mean, continuity? You should be measuring voltage across T/TV. 24 volts if open. 0 volts if closed. With the power off and testing T/TV, of course it will read continuity. Its coming through the relay coil.

109A_5 · October 25

Not sure what this means;

" i added heat pumps and besides winter it’s only supplying heat to hot water, and the low diff that is hard set on the Honeywell has it eating through propane for no reason 9 months of the year. "

The heat pumps supply your DHW (Domestic Hot Water) ? The boiler supplies your DHW ? Some other appliance supplies your DHW ?

Did the boiler supply the DHW at some point in time ?

Anyway, shut OFF the Boiler's and / or the system's power, All the power OFF !!! Remove the screw from the relay (Red circle) it does not belong there, and put it back where it belongs (Orange arrow) and secure it. Secure the screw at the Blue circle so it does not fall out. Restore the power. See if your problem goes away.

mattmia2 · October 25

that very likely is shorting the contact of the relay that it is sitting on

109A_5 · October 25

Also just FYI since you have an L8148E aquastat. It is a known issue that the solder joints that connect the relay (that the screw fell into) to the circuit board go bad with time and use. Since your aquastat appears to only control the burner, the symptoms would be no burner operation or intermittent burner operation. If you can solder the solder joints can be repaired. A Plumber or HVAC Tech will always change the whole aquastat.

gcubed · October 25

https://forum.heatinghelp.com/discussion/comment/1869132#Comment_1869132

Without being on the t-t they show open. If i disconnect the wires it does still fire.

https://forum.heatinghelp.com/discussion/comment/1869153#Comment_1869153

that previously the boiler was the only heat in the house, now the heating load has been greatly reduced (besides hot water, that’s still on the boiler). I just meant that for 9 months of the year the boiler is only supplying hot water and want to avoid it running multiple times a day to only keep itself at 180F.

Yikes on the screw, got that out and back in place plus the other one tightened down, will let you know if that fixes it. Have no idea how long that was sitting in that relay, noticed the empty hole but never paid attention to the screw.

https://forum.heatinghelp.com/discussion/comment/1869160#Comment_1869160

Thanks for the heads up, will watch for that

109A_5 · October 25

" I just meant that for 9 months of the year the boiler is only supplying hot water and want to avoid it running multiple times a day to only keep itself at 180F. "

With the aquastat's 'High Limit' being the only active limit, keeping the boiler water at 180 degrees, I suspect the boiler ran much more than what I would consider multiple times a day. I suspect your propane bill will go down a lot.

gcubed · October 25

https://forum.heatinghelp.com/discussion/comment/1869171#Comment_1869171

Hasn’t fired since I fixed that screw, so far so good.

yea, at least 10x a day and it was eating through my propane this summer. I have no idea how long the previous owners were just dealing with it running like that and paying the propane bill

Thank you so much, was going to replace the aquastat but was foiled by a little screw.

neilc · October 25

@109A_5 with the eyes,

good catch

mattmia2 · October 25

if that screw was just loose in the terminal it probably eventually worked loose from the vibration from the relay. It may have fallen in to the relay recently.

You can keep the solder joints on the relay from failing by using a couple dabs of silicone or hot glue to glue the base of the relay to the pcb so the shock of it opening and closing doesn't transfer in to the solder joints.

109A_5 · October 25

" I have no idea how long the previous owners were just dealing with it running like that and paying the propane bill "

I would have thought if that happened on the old owners watch they would have had it repaired since they would have noticed the fuel bill increase (at least in the non-heating months). Maybe that is part of the reason the house was sold. That's a lot of fuel $$$ going up the chimney.

" Called the company who serviced it prior and they were more than useless (was told yeah, that’s just how it is, it’s not cold start). "

Maybe the old owners got the same answer that @gcubed did that it was normal.

At least @gcubed figured out it was not normal and kept pursuing the issue.

109A_5 · October 25

https://forum.heatinghelp.com/discussion/comment/1869206#Comment_1869206

Securing the relay to the circuit board would certainly help. IMO the holes in the board for the relay pins are too large and the solder has to bridge that excessive large gap. Also for the mechanical mounting during assembly they just fold the relay leads over, this helps but the solder joints still fail. The solder joints of large and/or heavy items (or other mechanical stresses) that are just PCB mounted by their minimal pins often fail prematurely.

The few L8148 type aquastats that I have repaired, I remove the old solder, straiten the relay pins, rap some thin solid wire around the pins (often component lead cutoffs, about 22 AWG, whatever fits nice), squeeze it securely to the pins and snug to the circuit board, run it along the circuit board traces at least 1/2 inch, then solder the whole thing. Much more robust solder joint, may outlive the relay contacts.

Usually the hardest part is the dealing with the bulb in the immersion well and making sure the capillary tube does not touch anything electrical upon reassembly.

gcubed · October 26

https://forum.heatinghelp.com/discussion/comment/1869210#Comment_1869210

it’s been working exactly as it should today.

The only reason i think the old owners dealt with it for a while was on the sellers disclosure the amount of propane they stated they went through in a year was shockingly high. That coupled with the fact that they put in some hacky exhaust vent from that mechanicals room into the garage with the only purpose i can think of being to get the excessive hot air out of the room from the boiler running all the time. My cold water was warm as well as any water in the pipes would warm up due to the room being 85-90 all the time.

Besides saving all the money on the propane and not having to buy a new aquastat, it was exciting turning on the cold water in my kitchen sink and the water actually being cold.

109A_5 · October 26

Interesting, pulling air out of a boiler room due high ambient air temperatures may mess with the combustion air availability and flue draft. Probably not a good situation if not engineered correctly.

Also interesting how simple problems not repaired correctly turn into strange other issues.

Slantfin VHS-150 EP Aquastat

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