Gas boiler issue

JohnBoston

Hello,
My gas boiler heat is not working. I can't get a pro to come out until Monday or Tuesday and I am hoping that someone might be able to help me with troubleshooting in the meantime.

- One zone forced hot water cast iron radiators

- Utica boiler from 1996 (MGB150HD) with honeywell aquastat (L8148E)

- Nest thermostat running the last two years without problem (just 2 wires into tstat, red and white, no common wire but hasn't been a problem in 2 years and Nest says not needed to power this model.)

Radiators were cold this morning when we got up even though nest calls for heat. Manually changing the temp on the thermostat causes the relay in the aquastat to click but boiler didn't fire.

- I disconnected tstat and touched red/black wires together to see if the tstat was the problem. Same click in aquastat relay but again no boiler firing.

- Tried the same thing an hour or two later and after 20 times or so of touching red/white wires together the boiler fired up. Has been going for a few hours now bypassing the wall tstat. The temp. control at boiler stopped it (160 on dial in honeywell aquastat) and once the water cooled it started back up again.

I have young kids so am nervous about disconnecting the red/white wires and putting tstat back in line in case it doesn't start back up again. I have space heaters, so no one will freeze, but prefer not to use them if possible. I'm also not too happy about running the boiler when the wall tstat is bypassed.

I called the local heating guy who has worked on this boiler before and he said that it sounds like an electrical problem but the soonest I can get an electrician is probably Tuesday. I have a call out to another heating company but no call back.

Sorry for the long essay but do you have any suggestions as to what I could do in the meantime to trouble shoot?
I could pick up another aquastat tomorrow and start there but seems like a hack job to just throw parts at it.

Thanks

mattmia2

Pictures of the whole boiler, of the gas valve and controls. Does it have a vent damper?

JohnBoston

JohnBoston

mattmia2 said:

Pictures of the whole boiler, of the gas valve and controls. Does it have a vent damper?

Yes, it has a vent damper.

Jamie Hall

First thing that should happen after the click is the vent damper should open. Does it?

HVACNUT

Have you noticed if the circulator runs during these down times?
If the circulator doesn't run either, it could be the clapper relay not pulling in correctly and making good contact. Jumping red and white numerous times might have bumped it back into place.
You could turn off the power, and move the wires away from the relay. Easily lift the clapper and let it re seat.
It might be time for a new relay. There are much better aquastats out there. 
You don't need an electrician, you need a seasoned HVAC tech. 

JohnBoston

Jamie Hall said:

First thing that should happen after the click is the vent damper should open. Does it?

I'm almost positive that it did not. I was listening for the boiler to fire but I would have heard the damper move in the flue and it was silent.

The boiler is working now - but in wall tstat bypass. I dialed back the temp. in the aquastat from 160 to 130 so that we have heat until it can be repaired. Would that cause any problems running this way for a few days?

Maybe intermittent fault in the damper?

HVACNUT

Also the discoloration on the front draft hood is a little concerning. 
Make sure the wire that's running up behind there is connected to a spill switch and not just spliced through. 

EBEBRATT-Ed

First thing is Nest's are not reliable without a C...common wire. It may have worked the last couple of years but that should be fixed. It's not your problem now as you bypassed the stat wire but it will be some day. There are 100s of posts here on nest stats and they are always trouble.

Your problem could be a multitude of things, damper, gas valve, aquastat etc etc.

Sounds like an electrical problem but could be anything. You need a tchnician to go through this with a multimeter. What you don't want is someone guessing and being a parts changer.

unclejohn

Replace the aqua stat. 

JohnBoston

Thanks for all of the responses.

Update - I disconnected the tstat bypass last night as wasn't comfortable going to bed like that. i know there is the temp. switch in the aquastat but prefer to be safer.

This morning I sat next to the boiler while my wife put the tstat red/white wires together and waited a few seconds each time, and after about 10 times or so with nothing it fired up while I jiggled the relay a bit. I dont know if that was a coincidence or not but thinking it is the relay that is the problem and need a new aquastat.


To answer a few of the questions above
- Other than the relay clicking there is complete silence when it doesn't fire
- When it did fire the circ. came on, followed by damper opening, followed by boiler firing, so correct sequence.
- The discoloration on the front draft hood is very old and before my time. Was a concern for me too when I moved here but had it checked out.

HomerJSmith

I will tell you what I think. I've seen this many times. Taking something apart to see why a device fails give you invaluable diagnostic information.

The relay on the board opens and closes creating a vibration which translates to the solder connection on the back of the board. The pin that the relay is soldered to the board breaks the solder joint resulting in an intermittent performance or a total failure of the aquastat. This can be verified by removing the board and examining the relay solder joints. Be aware there are high voltages and low voltages that must be separated from each other.

The fix is to re solder the relay connections or replace the aquastat. Because of liability concerns professionals will replace the aquastat.

The relay is a two pole relay. One pole turns the circulator on and I believe it is not functioning. The other pole turns on the low voltage circuit, igniter, gas valve etc.

The two poles are on a reed switch and sometime they may not make contact when the relay closes. Also, the points sometimes get burned which can facilitate non closing of the points.

All the thermostat does is close the relay. You can manually close the relay by pressing the silver bar on top of the relay to the closed (activated) position. You might do this with a pencil using the eraser end.

mattmia2

I have seen that with many relays if the solder pads aren't designed right or if the leads aren't heated adequately when a board is wave soldered where a relay or even a component that only heats and cools will fatigue its way off the board.

JohnBoston

Update - changed out the aquastat yesterday for the same again and seems to have solved the issue - still calling for heat as needed from tstat 24 hrs later so fingers crossed.

I didn't think to look at the board/relay solder to see if there was anything obvious before it was trashed. Would have been more for interest sake as I would want to replace the unit rather than trust my solder.

From one of the above comments, I will look into adding a common wire. Seems like nest power stealing can be an issue long term. Would be very easy for me to run new tsat wire as easy access from wall and open bays in the basement. Where would you join the common in the boiler aquastat? - pics to follow

Thanks

JohnBoston