Stumped With Overheating Combi Boiler

HeatPav

I have a Westinghouse WBRCNG140W (Same as a HTP EFTC-140W and the same internal parts as a Mascot FT). It’s been running for about 4 years now since I bought it new and I have done minimal bi-annual maintenance on it, I never did a power flush of any sort. Towards the end of last winter, the heat started acting up to the point it no longer worked by the end of last season. Towards the end of last season, it started creating an explosive mess inside the cabinet and I could not (and still can’t) find where and how water was getting all over the place. I've stood watch a number of times hoping to catch it happen but no such luck. The DHW continued to work just OK but over the summer the temps began fluctuating but nothing too bad but it had been getting progressively worse towards the end of August.

With winter coming, I knew I had to get this repaired and prepped for the cold season. The first glaring problem I read was that it had to be the 3 Way Valve so I ordered one and replaced it. That seemed to fix the problem. I had CH & DHW and It worked great for nearly two weeks before the Combi started overheating. I thought the new 3-way valve went bad again but what was different this time was the CH worked fine but no DHW. When DHW was called for, the temps would zoom up and trip ER:16 overheat error. Meantime I had opened up the old 3 Way valve and I was pleasantly surprised how easily serviceable this was so I repaired it by cleaning the contacts, added epoxy to the worn-out lobes, loosened the sticky ball assembly and checked it with my multi-meter

and it all seemed fine. I then proceeded to rip everything out again and put back the old repaired 3-way valve but it did not help. I also read if it wasn’t the 3-way valve, it could be a clogged exchanger or bad board. I then replaced the board and it still overheated. During the wait for the new board, I flushed out both the CH and DHW and it was way worse than I expected. I was able to attach a garden hose to the intlet of the heat exchanger and another garden hose to the output of the DHW storage tank so the flow went through both. I used 1 gallon of vinegar to 4 gallons of water for a couple of hours, flushed with fresh water for a good hour and I then had a nice fast clear flow in both directions, meaning I swapped the hoses to make sure it was clear going in both directions, I also did the same with the DHW side too but not so long, it was pretty clean to begin with. The internal circulating pump seems to be fine, runs smoothly, not hot, no broken propellers and I can feel a smooth vibration as it ran.

So now I am stumped about what could possibly cause this overheating. When I first turn on the boiler, it will overheat right away to 200F (93C) but not trigger the error and it would work its way back down in temp. CH call does not trip the error and seems to work just fine, the temps remain normal. It only overheats when DHW is called. What I found is when I turn on CH and I then call for DHW, it does not overheat as long as there is cool temps from the zones flowing through the exchanger. I know the next thought would be the mixing valve but to me, that would make no sense since it is overheating on startup, before DHW is even called on. I created a color schematic for myself to help make sense of water flow and directions which I will attach below. I am at my wits-end with this boiler and I hope someone that is familiar with these combi boilers could share their thoughts and ideas, I would greatly appreciate it, thanks. For anyone who would like to look at a installation manual, just google whl-012.pdf or WBRCNG140W if that would help.

LRCCBJ

A very simple test:

Start with a cold boiler. Be sure CH is off (turn the stats down).

Put your hand on the #38 pipe. It should be cold. Leave your hand on the pipe.

Have someone else turn on the hot water…………full bore……….at a bathtub and have them leave their hand under the flowing water until they pull it away. Get a time for that (in seconds).

See how long it takes for you to remove your hand from that pipe (in seconds).

Observe how long it takes (in seconds) for the boiler to shutdown on limit (presumably 200F).

Report back with all three time measurements.

HeatPav

Thanks for your quick reply. I have an old Flir which helps and this is what it looks like. Not very warm in the DHW holding tank.

Grallert

I haver no experience with that boiler but maybe you could find the resistance readings for those temperature sensors and check those. Your boiler might not know what the water temperature is or what the outdoor temp is. Maybe a bad connection at the board?

HeatPav

Boy, that is what I am thinking too. It might not be the board but a bad connection to the board. I took a resistance reading of the dual sensors (CH and Overheat) and both showed resistance, not open, but I did not pay attention to the actual reading because I dont know the spec, I just wanted to make sure it wasnt open. But I will do that today and take some readings from Cool to Hot and see if resistance varies. Thanks.

Grallert

The resistance should change by how much is the question.

The rate might be the same for those types of resistors I don't know.

There might be a curve graph somewhere. The board then figures out what to do with those changing numbers.

hot_rod

The boiler racing to high temperature is often a lack of flow.

Plugged screen? Air still in the boiler or dhw HX? Circulator not running in the dhw mode.

HeatPav

Yeah, the boiler is racing to high but lack of flow from what is the question. Plugged screen? Not sure there is a screen, I haven't seen one anyway. Its been a battle with air on the DHW side and I dont know where this air is coming from but I am always discharging the air out of the air vent but never had an effect on anything each time I do. I am not sure if the circulator is suppose to run on DHW call but again, when the boiler is initialized from cold, it races to overheat before any call has been established.

GGross

Did you ever diagnose the leak inside the cabinet?

"Towards the end of last season, it started creating an explosive mess inside the cabinet and I could not (and still can’t) find where and how water was getting all over the place."

This is probably issue number 1 before you start (or continue) changing a bunch of parts. a massive leak is a serious problem. if the system is hooked to a fill valve you are adding a ton of air, a ton of fresh water which results in scale, these can impede flow or negatively affect the pump. The pump absolutely must flow through the boiler to transfer heat, whether a CH call or DHW call. the temp inside the unit rapidly coming up to its high limit indicates low flow, or poor heat transfer, and you have an issue active that can result in both. got to fix the leak first.

HeatPav

I haven't had the "explosive mess" since changing the 3-way valve, that seemed to have fixed it. It ran fine for two weeks without a mess inside the cabinet so it looks like the replacement solved that issue. You do bring up a good point however, I will turn off the fill valve and see if I lose pressure. I replaced all my gate valves with ball valves and the 4 loops do no leak, the pressure is remaining the same but I never checked the boiler itself, worth looking into, thanks for that.

HeatPav

@GGross I took your advice and despite thinking the circulating pump was good, I ripped it out and checked it anyway to make certain and sure enough, it was NOT working. This is a ridiculously priced pump, $400.00 and a week or longer (Thanksgiving week) before getting it. I decided I would purchased a 3 speed Grundfos UPS15-58FC pump from a local store for $138.00 and replaced flange part with the old boiler connections and seems to be working great now. The new pump has the same speed specs as the bad one. But now my concern is the explosive leak I had before and I now found where it was coming from. I found the upper exhaust pipe is leaking on the bottom horizontal side of the exhaust right before turning 90 degrees out of the cabinet. The pressure must of been so strong, it cracked the pipe somehow. This is so scary to think a exhaust pipe could have that must pressure that it would crack a plastic exhaust pipe. I have to quickly repair this before this acidic condensation destroys this inside. Thanks everyone for your help and responses.