Low Water cut Off

keyote

I decided to not install a flow switch on my new KHN 085 because they seem to have a lot of problems and i assumed the boiler had other safety's built in.and frankly i expect some pretty low flows at times that seemed while withing the boilers minimum would be out of range of a flow meter.
Now Im not so sure, I just noticed it talks about low water cutoff as an option and i kind of thought it was integral.what do you guys think. i was also thinking id prefer to leave make up closed and instal a alarm for low pressure but without a low water cutoff that scary.

Jamie Hall

There are a number of approaches to all this, however, think in terms of objectives:

Your safeties must be fail safe (fail operational is nice, but not feasible here). That is, if anything goes wrong with the boiler or the appurtenances or the safety devices, the boiler shuts down.

1. You need to shut the boiler down (this is one of the safeties) if there isn't enough circulation to handle the heat being generated.

2. You need to shut the boiler down if the boiler temperature goes too high (this is a backup to the aquastat).

3. You need to shut the boiler down if the boiler pressure goes too high.

4, You need to shut the boiler down if the water level in the boiler drops too low.

5. You need to shut the burner off in the event of a flameout (this should be already on the burner).

Note that a temperature/pressure relief valve will serve as a backup for 2 and 3, but should not be the only safety for those two.

If you have far more faith in machinery that I do, some of those could be automatic reset -- but I'd want a manual reset for all of them, so that somebody would have to at least look at the beast.

Tinman

Its a MUST on any mod con we install and a preferred method on cast iron too.

JUGHNE

Jamie, I don't believe there is a temp & pressure relief valve on hot water heating boiler. Only pressure from what I have seen. IMO.

Jamie Hall

JUGHNE said:

Jamie, I don't believe there is a temp & pressure relief valve on hot water heating boiler. Only pressure from what I have seen. IMO.

OK -- i need eddication here. I had thought that one needed both? At least on water heaters? But not on hot water boilers?

Only pressure on a hot water boiler?

JUGHNE

From what I have seen and read:

Boilers for heating only have pressure only relief valves. 30 PSI for hot water and 15 for steam. (small residential types, there are of course some bigger boys in the commercial areas, but we don't hear about them here very often)

Water heaters for DHW have the T&P, 100 to 150 PSI and 210 degrees for opening.

The heating boiler vessels are usually MAOP of maybe double of the PRV.

True DHW heaters are MAOP much higher, as they already have city pressure of maybe 40 to 100PSI pushing on them.

I have read here of some techs finding a WH T&P rated for the 100PSI/210degrees on home boilers.....that would have stopped that sucker from dripping, "I don't need no expurt"

If one of those 210 degree T&P's were stuck on any steam boiler, that would probably initiate a call to that "expurt", or 911.
IMHO, from a younger pup

keyote

the blow off is a pressure only [30 psi], however it has supply and return temperature sensors that the control monitors internally. shuts it down for over temp [185 reduces fan speed 195 shuts down] and too wide a delta t, dt50 reduces fan speed dt 60 shut down.
right off the unit is very crowded tridicator gauges, temp sensors, webstone purge valve unions. where can a low water cutoff be located?

Tinman

I install mine a few inches above the top of the boiler. Extra protection.

Tinman

Right above the ball valve on the supply is a tee with the bull of the tee looking back. That's where I put them.

hot_rod

keyote said:

I decided to not install a flow switch on my new KHN 085 because they seem to have a lot of problems and i assumed the boiler had other safety's built in.and frankly i expect some pretty low flows at times that seemed while withing the boilers minimum would be out of range of a flow meter.
Now Im not so sure, I just noticed it talks about low water cutoff as an option and i kind of thought it was integral.what do you guys think. i was also thinking id prefer to leave make up closed and instal a alarm for low pressure but without a low water cutoff that scary.

I think it does have a low pressure cutout as a safety also. I think it watches for a wide delta to shut down maybe?

Gordy

Redundancy in safety systems is always a good objective.

The boiler has its own built in features. However in water based systems you need to cover the possibility of system drain down through a leak.

The real danger is when the boiler of any flavor is above all radiation, or if a leak developed in the lowest part of the boiler piping when radiation is above boiler.

Tinman

All kinds of temperature safeties but I'm not aware of any low/delta pressure safeties .

JUGHNE

I personally feel that any boiler that one person can carry to the basement by their self alone does not have enough mass to stand fire inside it with out water and water moving.

My Lochinvar kbn 080 has a LWCO a few inches above the boiler itself. Yours may have a port inside the boiler for that connection of LWCO. (which seems too low to be effective)

I feel that my water tube boiler ( I assume that yours is a fire tube design) is like putting an oxcy/acetylene torch inside a coffee can.
If the water is not moving something bad is coming down.
There are temp sensors, but if no water to convey that temp quickly then there is a little more time to shutdown. So I feel that the first shutdown should be lack of water in the boiler, that would never require the temp sensor to be the actual cut-out.
What happens to a dry coffee pot?
BTWDIK.

Gordy

Most safeties are covered by the aquastat HL. If delta is to high temperature will climb rapidly to HL, and shut down. Pressure would be covered by pressure relief valve. I seem to recall some boilers of a mod/con variety, that do code out on low system pressure maybe they were combie boilers which monitor flow also.

Tinman

Right I was referring to low pressure safety.

JUGHNE

Early Munchkins has a pressure sensor to prevent operation without a minimum available. Seemed like a good feature but perhaps became unreliable as it aged.

keyote

thinking of using this taco LTR series, has fancy lights, any one know how long that harness is im going to have to squeeze this is about 32' from boiler and would need a 5' harness to the panel. I cant get it higher than boiler my supply pipe come straight out horizontally but it will be a couple feet down the supply stub out. seems like that top of HX.Ill mount it horizontally so at least it will trigger if pipe less than half full that ought to catch it in time.If i go up the riser ill be downstream of the pumps spring check.damn i wish i caught this sooner youde think well i would think they would put one integrally for the cost of the boiler.

Tinman

The Lochinvar LWCO for the Knights is a Taco control with the proper plug and play connector.

keyote

the LTR is a taco with the plug but could not find length of fancy plug anywhere and its not a stock item this guard dog also has a lochinvar plug n play seems similar seeing who can get back to me first with harness length

hot_rod

No harm in adding a low water cutout, code in your area may require it. They need to be tested from time to time, and the probe cleaned if you use hard water

The boiler has an operating and high limit temperature control, flow switch, flue temperature lockout and it does watch for wide delta. A red screen flashes under any of the fail conditions.

The flow switch should protect for a dry or air locked condition and the 240F flue sensor would trip quickly on a dry boiler.

The control also logs error codes to help troubleshoot.

The Gionommi style had a pressure switch on the header.

Boon

I spoke with tech support about this. The KHN085 does not have an integral LWCO; it is jumped on the low voltage board. The Lochinvar's LWCO part number is WTR20009, and the instructions (INS70045 02/09 Rev A) do not specify where to install the LWCO on the KHNs, so again, I consulted tech support who told me to install it under the relief valve on a tee.



Please forgive the rat's nest of wire I haven't tidy'd up or insulated yet.

hot_rod

If it is a probe type, but to put it where it gets flow across it. In a dead end, high spot you may get nuisance lockouts.

keyote

LMAOROTF %&$#@!&
I had that same tee idea but decided it might not work might get an air lock so i just ten minutes ago cut into my header to scrounge 3 linear inches in the only place i could find it going to be a **** to finish. ^%$#&@&

That lochinvar part seems to be 250. about triple taco or mcdonnell douglas am i missing something? the guard dog has a harness specifically for loch knight boilers. di they caution you to use theirs only or anything?

Jamie Hall

All very interesting...

Anyone know what the failure modes on all these electronic gadgets are? Not what things going wrong in the boiler are they expected to guard against, but what things can go wrong in the controls themselves, and what happens when they do?

Jean-David Beyer

My W-M claims it has protection for low water detection that may be approved in certain localities. I am convinced it should be enough. But my inspector is not convinced, so I have an external one also installed a little above where the water returns to the boiler (of an Ultra-3).