High limit error on Noritz combi boiler when using radiant heating

JaySyd

Hi All, happy TG to everyone here!

We've been having an issue with our combi boiler where after running radiant heating fine through the previous day, the next morning when we wake up and run the domestic hot water for showers etc, the boiler trips with a high limit error code 20. The only solution is to pull up the pressure relief at the top of the boiler and release pressure, reset the unit and things get running again.

Why would this be happening every day? I've purged the system of what I think is any air in the loops but it keeps happening.

This never happens if the heating isn't running and we are only using domestic hot water (during summer etc) 

Any thoughts?

Thank you! 

Ironman

How about posting some pics that show the boiler and the piping around it?

JaySyd

@Ironman Sorry forgot to post images - see some attached of the boiler and the heating loops + circulators

HomerJSmith

How long have you had this issue? When did it start? Have you made any changes to the system? Has any electrical breakers been tripped or switches switched? Pics showing all the piping with better lighting would be helpful.

JaySyd

@HomerJSmith thanks for the questions. This actually happened a few times last winter season but only every few weeks/months - so I didnt think anything of it. Unfortunately this season it's been every night. I have a pro coming out next week to take a look but it's not an issue that's easily replicated and it seems to only happen after the heating has been running for a full day + night.

Just wonder if its the pressure relief valve at the top of the boiler gone bad and not regulating the pressure from the 180 degree heating water temp and the unit is shutting off as the pressure has built up too much. 

Ironman

The high limit shutdown is from sensing the water temperature is too high. The relief valve doesn’t sense temperature; it relieves when the pressure is too high.

There may be a common cause for both.

HomerJSmith

This appears to have been a growing problem as if something is gradually failing. What is the quality of water in terms of hardness? Follow the trouble shooting solutions Noritz publishes.

Unplug the power to the unit for about 2 minutes and the plug the unit back in. You would be surprised at how that little trick can restore proper operation in electrical gadgets.

JaySyd

Thanks alot guys for the suggestions. Tried a number of power cycles on the boiler as that is needed anyway to get rid of the 20 error code. Issue still comes back.

I did a descale / flush on both domestic and heating sides of the boiler about 1 month ago but that seems like it didn't really do the trick.

I'll post an update once the vendor comes onsite to take a look - thanks again all. 

hot_rod

If in fact that boiler senses a high pressure condition and shuts down, I would check the expansion tank, see if it is waterlogged. That could cause the pressure increase.

If the relief trips on it's own and pressure drops, it could go into lockout. Low pressure protection is common on many boilers. I've not heard of high pressure cutout protection??

Alan (California Radiant) Forbes

It seems to be a high temperature issue, not high pressure. Have you tested or replaced the sensor?

What is the model number of the Noritz?

HomerJSmith

Is it high pressure or high temperature? Increasing high pressure ultimately pushes water out of the pressure relief valve. I would want a separate measure of temperature to verify the boiler temperature. A check of accuracy. Trust but verify. Sensor do go awry. Was the de-scaling job effective? What about the flow? *****What's the model# of your boiler?*****

HomerJSmith

Did you loosen the air vent cap at the internal pump and let air out during purging?
An over temperature condition in a boiler is usually an over firing or not enough flow thru the HX. I would look at the flow if the sensor and de-scaling is correct. Pics of your sys would be a great idea at this point in time.

May apply:

Alan (California Radiant) Forbes

@HomerJSmith
@JaySyd said:

We've been having an issue with our combi boiler where after running radiant heating fine through the previous day, the next morning when we wake up and run the domestic hot water for showers etc, the boiler trips with a high limit error code 20.

I was thinking that it might be a flow issue as well, but it happens on a call for DHW when there's usually good or adequate flow and a high ΔT. I still think it's a sensor issue.

HomerJSmith

This link may help! https://forum.heatinghelp.com/discussion/161210/noritz-combi-nightmare

JaySyd

Thanks everyone for your help and suggestions. The solution to the error code 20 was a full air purge / flush of all loops. We had no way to isolate loops and feed them (since the auto Feeder only comes on when the boiler opens a valve when it senses low pressure.) - so the plumber installed a fill valve. Problem seems solved for now, but it's uncovered another issue with a potential leak in the system. We know this because we fill it to 20 pounds and then after running the system for 0.5 to 1 days, the pressure drops to 5 pounds or so and then the system errors with. 57 (low water pressure) error. The saga continues.... 

JaySyd

HomerJSmith said:

This link may help! https://forum.heatinghelp.com/discussion/161210/noritz-combi-nightmare

This pretty much describes what we are now dealing with after dealing with the error code 20.i guess a call to Noritz tomorrow is in order! Thank you sir.