That's the problem -- all of these conditions you're referring to are supposed to be reflected on the screen. But there aren't any! The status is simply "Standby" and something like 85° or 90°F...

In other words, as far the controller is concerned, there is nothing wrong... It is not, that it is trying to heat it up and failing. It is not even trying... Some times...

"It may be time to find someone else who is proficient in boiler repair." Mike is right, if they gave up you should certainly give up on them.

It's not difficult to find the problem but your service tech has no obvious troubleshooting skills and unable to read or understand wiring, ladder and logic diagrams to find the problem. A competent tech would have no problem finding the problem so find someone qualified.

Either the controller isn't getting a input signal or it's not generating an output signal.

The error codes on most HVAC diagnostic displays are not fool proof. You could have an error condition that the software does not recognize. Boilers were providing heating and hot water for about 100 years before the diagnostic screen appeared. Some how HVAC techs were able to identify problems and fix them.

I gather this is an intermittent problem. This makes it difficult to troubleshoot. You increase your chances of fixing it if you can make it fail reliably. Does it ever fail when the boiler is serving the heating zones?

Based on what you have said so far, my guess is this is a control board issue. Did the tech measure the supply voltage to the control board under all operating conditions? Electronic equipment will do strange things when the power supply is out of range. If everything outside the control has been verified as working, then I would replace the control board before replacing the whole boiler. I suppose the repair company does not want to do this because they can't return electronic parts if it is not the problem.

If the status is standby, then that would indicate that the system is receiving no demand signal (see page 40). So it's not heating because it doesn't see the request.

You say you're cranking the domestic hot water to 195°, but page 46 would indicate that that is outside the allowable range for the setppint (134°-189°) ... are you sure you're modifying the correct setpoint? Or might you be playing with central heating and expecting results for domestic hot water.

You said they won't call the manufacturer without an error code, but have you tried calling the manufacturer?

Out of curiosity, when you say it only sometimes has an issue, is there a pattern to when it won't work? Is it always under the same conditions or random? Like does it work better on warm days or cold days? Does it matter what is requesting hot water? It's easier to troubleshoot if you know what instances create the trouble. I would be keeping notes on when it fauls and what conditions were.

> Does it ever fail when the boiler is serving the heating zones?

The problem started after the heating ended -- in late April. We didn't need to heat this fall yet...

> my guess is this is a control board issue.

They did suggest replacing the control unit, yes. But then, upon seeing the display working, withdrew the suggestion... The new unit for this boiler is over $500, so I'm hesitant to "just go and buy it" -- without any certainty, that it will help.

No, no one measured any voltages...

@BlueberryBundtcake - 6a/5b MA, answering your questions:

> it's not heating because it doesn't see the request.

Ok, but is it not supposed to maintain a certain temperature -- just in case someone requests it? I know, it did maintain it for 10 years before... Again, it knows, the current temperature is low -- it just does not do anything about it...

> but page 46 would indicate that that is outside the allowable range for the setppint (134°-189°)

Yes, I think, you're right -- 189° it is. I just remember going all the way to maximum, whatever it is.

> but have you tried calling the manufacturer?

Yes. The company wouldn't talk to "the homeowner". Only to the "HVAC professional".

> is there a pattern to when it won't work?

I think, the water cools down from not being used -- such as overnight. I'm the last one to take shower in the morning, for example, so my water is always hot. But the mistress of my thoughts is usually the first to take it, and it is nearly-always cold.

A normal temperature for a water heater setting is 110°, so maintaining a temperature of 80° for standby when not heating the house, isn't outrageous. When you need to heat your house, of course you need warmer water held, but when that's not necessary, you only need water heated for domestic hot water usage. I'm wondering if you're running into issues related to mild weather operation settings.

I'm also thinking you may be playing with a maximum rather than request temperature, which would explain why it doesn't react to your changing the value: 80° is below 189° just as it was below whatever the previous maximum, so there's no change in what's needed.

I would have expected them to test voltages, or at least resistances, since numbers are given for expected values on page 51 ... I mean, whenever there might be an issue with a sensor/thermistor, checking values with a multimeter seems like a go to if expected values are given.

They did the major service, right? Do they know what they updated or changed? Did they change a value somewhere? I know when we had our water heater replaced the person told us what setting our previous unit was at and what temperature he was obligated to set the new one to ... (we did inch it up to 113°, because one of the showers is on a really long run, and we don't mind/know to be careful with extra hot kitchen faucet (not scalding hot ... just hotter than normal).

They certainly didn't change any settings deliberately. I suspect, there was an inadvertent change...

85° is way too low for DHW, in our opinion. How do I raise the minimum?

You are failing to answer the questions asked of you DOOFUS, without the information requested little can be done to help you "Does it ever fail when the boiler is serving the heating zones?" YOU need to test the heating mode but it must be done when the temperature is low enough outside to allow the heat mode to fire up the boiler. Default temperature is 70 degrees, but we don't know what the actual set temp is.

You had serious service work done. What work was done and it needs to be specific, like the initial problem and what they did, check your bill.

How do I raise the minimum? The answer is in the manual linked by you and requires entering the setting menu. Have you entered the menu yet and looked at or changed anything? You could be the problem if you changed something. Did you enter the installer menu and then initiate the system test? And was the test turned off? See BIG warning notice on page 48. "Be sure to set the System Test parameter back to “Off” before leaving the installation. Otherwise, problems with cycling or insufficient heat may occur."

Without a complete understanding of section 8 in the manual I don't think you should change a thing until knowing what to do. Changing one minor setting by mistake could totally shut down your boiler. Example: "Yes, I think, you're right -- 189° it is. I just remember going all the way to maximum, whatever it is."

View the setting only without changing a thing and write them all down, then post all the settings along with Blocking error history and Locking error history. (if you have the letter "E" or "A" displayed on the controller you have a blocking or locking error stored in history.) People need information and it's your duty to supply it.

I think, the water cools down from not being used -- such as overnight. I'm the last one to take shower in the morning, for example, so my water is always hot. But the mistress of my thoughts is usually the first to take it, and it is nearly-always cold.

Do this behavior of cold water with the first shower, but hot with the last shower happen everyday? This is the opposite behavior of a hot water tank. Perhaps the problem is with the hot water storage tank and not the boiler.

Has the tank ever been flushed? Do you live in a area with hard water? How old is the tank?

@mike_home, the tank was installed together with the boiler -- in 2010. I don't think, it was ever flushed.

The city water is not too hard, and we use a house-wide water-softener...

You didn't answer the first question. Does the behavior of having the water heater supplying colder water for the initial shower, and then providing hotter water on subsequent showers occur everyday?

Does the display actively indicate the water temperature? For example does it show it is 85 degrees in the early morning, and then indicates a higher temperature after additional showers?

I think, it does occur every day, but we cannot say for sure. There are many people in the house -- including tenants using the same heater.

Don't know the exact answer to the second question either -- we don't always go there to check. 85° is the lowest I've seen on the display in months -- usually it is higher.

The key to diagnosing issues is good data keeping ... if you aren't checking with any consistancy or pattern, it's harder to tell what is going on and you won't have any way to form correlations.

So if it's usually higher, whatis it usually? This one time it was 85°, what were the conditions? What was the approximate temperature? (40s? 50s? 60s? 70s? 80s?) Whattime of day was it? What was going on with water, as much as you know?

Is it better or worse when there are multiple water users? Are some fixtures better than others in terms of temperature?

All fixtures are same, when this happens. The water is lukewarm. What we think -- as I already posted -- is that the water slowly cools down in the tank without being reheated (kept hot).

When we drain it -- such as by someone taking a cold(er) shower, it eventually begins running hot (as in, needs to be mixed with cold water to be usable). So, yeah, multiple people using it seem to improve things...

If my suspicion of some logical error -- rather than physical malfunction -- is correct, the problem will disappear, when the heating begins. But we are afraid to wait that long -- and then start replacing the boiler... :-(

Ok, mystery solved -- the setting on the water tank was set low, overwriting the boiler's...

I took another look at the document you posted. I found the table describing the domestic hot water modes. Is your boiler set up in mode 1 or 2?

So I gather from this the how water heater has it own temperature sensor and tells the boiler the hot water temperature has dropped. I am curious how you were able to figure this out when the HVAC tech's solution was to replace the boiler.

> I am curious how you were able to figure this out

We started inviting bids for the boiler-replacement and one of the pros, who came to give estimate, told me about the heater's own max-temperature setting...

It is nice to hear there are HVAC professionals who are both honest and competent. You should consider calling this company for your future HVAC servicing.