Honeywell L4006A not working as intended?

JoeChan

We have a steam system with a hot water zone attached to supply an indirect hot water heater. That indirect feeds a hot water and a radiant zone. The system was installed back in April, and only now do we get some serious use of it. This morning, I found that the loop between the boiler and the indirect started to bang. It sounded to me like the water is boiling in the pipes. After experimenting with it a bit, I found the following:



- From a cold start, the pipes never bangs, the boiler shuts off at 140 as set on the honeywell aquastat.



- From a cold start, even if the steam and hot water zones are calling at the same time, the pipes don't bang.



- From a hot start (the steam zone just stopped calling), the hot water zone if turned on, will turn on the boiler, and banging starts a couple of minutes after that.



When I looked up the spec for L4006A, it says that it only breaks the circuit on temperature rise. This sort of agrees with the behavior I observed: if the boiler is already hot, the water will be above 140, and L4006A never shuts off the boiler, which leads to boiling water in the pipes. If my hypothesis is correct, how should it be fixed?

Steamhead

I suspect a piping issue

when the pump starts it drops the pressure on the water at the inlet, and if the boiler is hot this can make the water flash to steam and bang. This is also not good for the pump.



The cure is a bypass which recirculates some cooler return water back into the pump. This will cool the water at the inlet enough so it won't flash to steam when the pump starts.



Another issue might be that the circulator is mounted too high, so it doesn't have the weight of the water in the boiler giving it enough standing pressure at the inlet.



We have several of these setups in the field and they work well. Here's one of them- the hot-water loop on this one feeds an indirect water heater rather than baseboard, but the principles are the same:



http://www.heatinghelp.com/forum-thread/132567/One-of-the-worst-maintained-oil-fired-boilers-weve-seen



Take some pictures of your boiler and the piping that feeds and returns from the loop and post them here so we can have a look.

JoeChan

May be more than piping?

May be piping is one problem, but that doesn't explain why the boiler got turned on when the hot water zone calls even when the the boiler water is well above 140. Attached is the picture that shows our set up. There is no bypass from the return to the supply. The circulator is mounted just below the boiler. There are check valves on both the supply and return side of the hot water loop that feeds the indirect hot water heater.



One other bit of info that may be useful. We have a vapor vacuum system with a Hoffman differential loop. It cuts out at about 6oz. The main vent is a vacuum vent, but we didn't notice it in the past because the radiators are a bit leaky. We replaced all the steam traps at the same time we added the new zones, and now it is actually holds a good vacuum for hours. (The pressure gages are running backwards when the boiler cuts out.) I wonder if the vacuum is also making the water boil at a lower temperature, and compounds the problem.

Steamhead

Aquastat is in the wrong place

it should be mounted on the tee where the hot water leaves the boiler on its way to the circulator. It can't sense anything where it is. Look at the aquastat location in my thread to see how it's done.



Also, that circulator won't last long. Wet-rotor circs don't like the harsh water in a steam boiler. You should use an oil-lubed bronze one like the B&G 100AB in my thread- even though they're more expensive.



And you do need a bypass. We typically install a 3/4" bypass with a stop (not ball or gate) valve in it. This lets us adjust the amount of water going thru the bypass.



What make and model is your boiler?

JoeChan

The boiler is Weil-McLain EG Series 4

We had that circulator for about 12 years now, although it use to only drive a small hot water zone to the basement bedroom, which was on may be once a year. Now that it is driving two other zones, I afraid we may have to repipe it.