System 2000 EK1 High Limit Aquastat Operation

NEMatt

While I don't have a "problem" with my EK1 producing hot water or (now that it is getting chilly) heating the house, it seems like it runs up against the high limit aquastat more often than one would think.

This mostly occurs with hot water heater calls, and depends how hot the boiler itself already was.

As an example: I came home today and bumped the upstairs heat two degrees. From essentially dead cold boiler it took 8 min to satisfy the call. Didn't hit the high limit as the room thermostat reached setpoint when the boiler T&P gauge was at about 200.

However maybe 5 minutes afterward my wife took a shower which ultimately resulted in a hot water call. The boiler ran up against the high limit (215) once, coasted back down, re-lit, and nearly hit the high limit again before the tank aquastat was satisfied.

This doesn't seem entirely normal, though there is no shortage of heat or hot water.

Thoughts?

EdTheHeaterMan

The main problem with any oil-fired system is that they can't make them small enough. The oil flame in those things gets to be near 2800° and making the flame smaller than 70,000 BTUs is problematic. That said, The EK boilers are one of the best I've seen at getting it right in small BTU load homes.

The fact that the boiler is getting that hot that fast is a testament to the efficiency of the burner and boiler combination. Wait until there's a real load on the system, in the dead of winter. I believe you will be satisfied with the operation at that point. This time if the season the burner runs with the same flame that you need for the coldest day of the year. Since you won't need anywhere near that many BTUs now, the high limit will be reached more often.

You do have an option to lower the high limit to say 200°, but ask your installer about that. Most who sell EK are factory trained to some extent and are usually very knowledgeable on the subject.

EzzyT

How old is the boiler and when was the last time the flat plate heat exchanger was flushed out with scale remover? Typically if your hitting high limit on when the domestic zone is calling then it’s a restriction on the flat plate hess as t exchanger and might need to be replaced.

HVACNUT

The Energy Manager isn't showing a code? The only way to operate off the high limit is if there's a problem with the return temperature sensor or the Manager itself. 
In the meantime, turn the high limit down to 160° until the issue is resolved. 

NEMatt

Ezzy.  2009.  Not sure if the PHE was ever replaced or if the boiler side was ever cleaned.  We bought the place a couple months ago.  DHW side I flushed recently.

HVACNUT.  No codes.  Acts normally other than this. How hot should the system be running?  It only opens the zone when the return is 140 so it would hardly run if the output limit was 160.  Zone would either be closed or burner would be shut off.

szwedj

Like EzzyT recommended, I would start by flushing the plate heat exchanger, particularly the boiler side of the plate. Typically the plate is located in the boilers bypass circuit, so during a domestic hot water call, all the full is through that bypass, if the flow becomes restricted, it can cause the system can trip on the high limit. It may not be as noticeable during a heat call because once the heating zone opens there is additional flow through that zone and not just through the boilers bypass.

NEMatt

Joe, I'm guessing the heat exchanger needs to come off the boiler to flush that side of it?  Doing the domestic side was easy.

szwedj

NEMatt Correct. The domestic side sees constant raw water and is setup to back flush very easily. The boiler side is closed and typically treated so most of the time there are no issues. But sometimes overtime it may need to be backflushed or cleaned too.

HVACNUT

The tridicator reads SWT, the Manager reads RWT. Is the tridicator reading correctly? Again, if the boiler is truly running off the high limit, the Manager should be showing a 190 code. Maybe check the bypass. 

NEMatt

HVACNUT, sorry didn't know the official term of the temp and pressure gauge. So yes, I do believe the tridicator is correct and I believe it is tripping off the high limit since it shuts the burner down precisely as that needle hits 215F. Pressure remains around 23psi when hot.

This is the non-LCD/button manager so no error codes shown. I guess it has that little port to connect but no idea what that goes to.

szwedj

HVACNUT While you are correct, what you need to think about is during preheat, all the flow is through the boiler bypass. While the managers sensor is in the boilers return, it is located down stream of the plate in the bypass, if the flow get restricted or blocked, the return sensor doesn't see how hot the water or at least not before the safety high can trip.

NEMatt

What should the supply temp actually be? I guess I am failing to understand why the energy manager would even have light bars that indicate a 190F return if the supply wasn't able to run in excess of 200 without it being a problem.

This morning I moved the temp from like 64 overnight to 67 to get some heat in the house. As above, the boiler was dead cold as was the heating circuit water. Boiler had to open and shut the zone valve a few times as the cold water in the lines dropped the temp then it recovered to 140 and reopened. Normal operation. Once the return water remained in excess of 120 or whatever it is to keep the valve open all the time, both the tridicator and return temp bars kept climbing together. High limit was reached when the bars were all the way to the top or one bar from the top. This I think is just a case of the radiators becoming heat soaked and the room simply can't accept heat as fast as the boiler is producing it.

If running into the limit aquastat is a "fault", I'm not sure what is supposed to regulate the boiler's upper run state.

szwedj

The system manager is the operating aquastat and it functions based on return temperature. If the return temp gets up to 170deg (or 190deg if option switch 9 is on) the manager will shut the burner off. Basically at that point you are not stripping the heat from the boiler. Some examples could be an under radiated heating zone or if the domestic side of the plate has a flow restriction. The high light will typically trip when the is a lack of flow on the boiler side. Some examples could be a bad system circ or a boiler side blockage/restriction.

NEMatt

Ok that makes more sense. For DHW calls it most definitely does not operate off the return aquastat as you mentioned. Return never gets that hot.

With heating calls it will sometimes do that, where the return temp aquastat turns the burner off (light goes out).

szwedj

So, If during the DHW call the burner is shutting off on high limit (and the burner light is still lit on the manager), you are looking at a flow restriction on the boiler side, in this case most likely the boiler side of the plate.

NEMatt

Thanks. And because the high limit switch is in the bypass after the heat exchanger you think bit of blockage could also be triggering it during heating operation under certain circumstances? I'm guessing it flows through both at the same time during heating calls.