Boiler knocking

Fontana

Utica SFH4150WT oil fired base board..New Honeywell aquastat L7224U..High Limit set 180° with 10° differential...When a zone calls for heat furnace turns on and runs till the 180 limit..At about 175 it starts to make a knocking noise rising in sound and speed and goes on for about 30 seconds after high limit shut off then ceases..This started last year prior to new aquastat.. Noticed the boiler water temp will rise to about 190 in a few minutes and drop as zone uses the water eventually to the 170 start up.. I searched here and gleaned what I could..Went and checked expansion tank for heat and is hot only in top 1/4..Boiler pressure will go from 15 psi to 20 at max temp and then drop down as boiler cools..Oil Service says getting too hot and is boiling [like in an area]? Say to reduce temperature? I did reduce high limit to 175 and seemed to help some, as far as how loud the knocks are..Sorry for long post, tried to give as much info as I could..Thanks, Seb..

Jamie Hall

Not an expert on hydronics -- hopefully one will come on board here -- but if I had to bet, I'd bet on localised boiling in the boiler. Which leads me to wonder: do you have enough circulation through the boiler?

Fontana

Localised, thats what I was trying to say..Once the furnace shuts off the boiling is dissipated to the rest of the water which is probably why I noted the temp rise after shut off and the noise dissipating...I questioned the Service guy as to why it could be localised; boiler eroding, liner eroding, ect and never got an answer other than liner was fine..Thanks, Seb..

Brewbeer

Can you describe the type of burner and oil nozzle size? Circulator and system piping?

Fontana

Burner is Becket, model AFG..Nozzle is 1.00 [max 1.5], 80° angle,B spray. Efficiency runs consistent 82.5%..One circulator and 5 zones. 1" main lines "trunk" with 3/4 through base boards and unit heaters in garage except one zone is 5/8ths Pex to base board..I have to note that system had been working fine as set up [about 6 years] till last year when the noise started..Two zones hardly ever come on, Garage average run time is about 7 minutes an hour and the other two house zones will vary with if the wife has the fireplace going..House is about 1500 sq ft..

Fontana

I have "stand" pipes in every zone line and trunk lines with manual bleeder, the kind with a key, seven in all plus the Taco Air Scoop which has a bleeder on top plus another bleeder at top of boiler...No air comes out of any now; they did there job when the domestic coil was replaced and the new Aquastat installed in December 2015 and in the past adding zone(s)...I have mentioned that system was ok for about 6 years, when I would turn the heat on in the fall [october] and the heat would cycle some I'd go around and bleed all the bleeders and would get a tiny bit of air and any time I checked be fine the rest of the heating season..Oil Service guy made no mention of possible air in the lines....

STEVEusaPA

Your temperature gauge/aquastat may be incorrect and the temperature is getting up to the boiling point, or hot enough that you hear crud inside popping

Jamie Hall

STEVEusaPA said:

Your temperature gauge/aquastat may be incorrect and the temperature is getting up to the boiling point, or hot enough that you hear crud inside popping

It might not even have to be that inaccurate. Depending very much on how water circulates in the boiler, if the flow through the boiler is too low (I don't think that that's been answered yet) it is possible for localised hot spots to form and pop.

Fontana

Gauge and Aquastat brand new..Temp swing verified with infrared temp gauge...The only thing I can't say is if the flow rate is right or wrong..Boiler temp rises slower than it falls during the call for heat cycle which seems to be in the right correlation... Could the circulator impellor be worn out; or erroded as its the only thing that hasn't been changed ? How would I verify the flow rate? Thanks, Seb.

billtwocase

Try Crystal Clear from Sids, and replace the extrol tank is where I would start. A .85 nozzle in that boiler at 140 PSI is more than sufficient

Fontana

billtwocase said:

Try Crystal Clear from Sids, and replace the extrol tank is where I would start. A .85 nozzle in that boiler at 140 PSI is more than sufficient

You mean 140°?

Ironman

Fontana said:

billtwocase said:

Try Crystal Clear from Sids, and replace the extrol tank is where I would start. A .85 nozzle in that boiler at 140 PSI is more than sufficient

You mean 140°?

No, he means 140 psi oil pressure to the nozzle.

Fontana

Ironman said:

Fontana said:

billtwocase said:

Try Crystal Clear from Sids, and replace the extrol tank is where I would start. A .85 nozzle in that boiler at 140 PSI is more than sufficient

You mean 140°?

No, he means 140 psi oil pressure to the nozzle.

Ah, got it..Should I check the pressure at the Extrol tank? If water comes out then there is a problem with it?

billtwocase

Thanks Bob, yes the pump pressure should already be at 140 on that, unless it was altered. With zero pressure on the boiler, there should be 15 PSI air in the Extrol, and NO water should come out of the valve stem. If it is an Amtrol Extrol manufactured within the last 6-7 years, **** can it. They are failing constantly, for me anyways. Try a Watts 30 instead. I have had good results so far with them.

Fontana

billtwocase said:

Thanks Bob, yes the pump pressure should already be at 140 on that, unless it was altered. With zero pressure on the boiler, there should be 15 PSI air in the Extrol, and NO water should come out of the valve stem. If it is an Amtrol Extrol manufactured within the last 6-7 years, **** can it. They are failing constantly, for me anyways. Try a Watts 30 instead. I have had good results so far with them.

I will check it out later today...Still noting boiler temp rises 10° after high temp shut off...Thanks, Seb.

billtwocase

It is common for that, and other boilers to gain temp by means of residual, just have to set your aquastat with that in mind.

Fontana

billtwocase said:

It is common for that, and other boilers to gain temp by means of residual, just have to set your aquastat with that in mind.

Ok..

Fontana

I checked expansion tank for air pressure and it was at 15 psi..No evidence of water at the valve..Any way to check circulating pump for flow with out removing it? If I drop the high limit to 170° is that still hot enough?

Fontana

Fontana said:

I checked expansion tank for air pressure and it was at 15 psi..No evidence of water at the valve..Any way to check circulating pump for flow with out removing it? If I drop the high limit to 170° is that still hot enough?

Any comments? House is base board and garage is hanging unit heater [crane]..Thanks, Seb..

Fontana

I have lowered the boiler high limit to 170° but the knocking persists..Still starts after about the first 5° of temperature rise and continues as long as the burner runs, after burner stops the knocking dissapates in a bout 30 seconds or so..Any new ideas? Driving me nuts..Seb..

Ironman

Does, or has, the system had any on-going leaks? If so, there could be a scale build up which can cause the water to boil in the scale pockets.

hot_rod

You may need to descale the boiler, I have used Hercules Sizzle to remedy problems like this on copper and cast boilers. I too would look for a leak causing water make up.

In old water heaters that noise is sometimes caller percolation, where the flame is heating a mineral layer in the bottom.

lchmb

Could be as simple as minerals in the system. Mine did the same thing, added a bottle of 8 way and calmed it down in a week..like other's mention though, are you bringing in fresh water?

Fontana

I have checked for leaks every where..I can't find any thing..Little crud at a fitting or facet packing or two but no drips....How would I add any 8-way or Hercules Sizzle and how doe the stuff work? Have to drain and refill system? I would have thought the service guy would have suggested something..If the circulating pump is is bad [how would I tell?] like maybe an impeller that worn out or something weird..

hot_rod

The Hercules product is an acid, add as per directions, circulate, drain and flush, refill and check ph with the included test strip. It is a multi step process. You would need a pump or means to inject the product, might be best left to a pro?

Some of the other products get injected and left in the system, typically the keep the minerals in suspension, to eliminate to percolation.

I believe the Rectorseal 8 way is a caustic soda, it would be added, circulated and flushed also.

But first narrow down the cause, a pump noise would be a different fix. Scaled boilers usually happen over a period of time, whereas a failed pump may just show up one day.

There is no harm in a boiler cleaning, flush and refill, but it may not be the fix.

If you do the cleaner, check the hardness of the fill water you have, some suggest anything over 8-10 grains should be treated, or buy DI water and fill the system.


How old is the system, when did the noise start?

Fontana

Noise started with start up of 2015 season..Furnace off all summer, started noise again with start up of 2016 season..Memory just jogged, the domestic water coil gasket was leaking some but again only enough to show some evidence, I shut water off at all valves for the summer and had no water leakage..Had the coil replaced beginning of 2016 and new Aquastat..System is probably 20 yrs old..

Paul48

Well water? If so, is it hard?

Fontana

Yes well water..I would have to say that it is not hard, never any internal build up in system pipes..Do have a water softner but is only hooked up to domestic lines, no non domestic sinks, out side water, or furnace..

hot_rod

The box stores have test strips for around 10- 15 bucks. It would be a good idea to see how your water measures for hardness. Hardness can vary widely.

Google water hardness testing and see some simple tests with just soap in a glass of water.

Here is an example for Canadian water hardness.

If you are going through the process of cleaning the system, you want to make sure you put good quality water back in.

htpp://funkyfluff.co/water-hardness-in-canada/

EdTheHeaterMan

This is a shot in the dark but I had a noise problem years ago with a 4 zone (4 Circulators) system. One of the circulators was installed backwards during a repair. As it turned out if other zones were calling everything was fine. If the backwards zone was the only zone calling the water was reversed thru the boiler causing the water to return thru the supply and feed thru the return. The limit control was getting return water temperature when the water flowed backwards. The boiler overheated and the system had a banging like you could not imagine. Check the arrow on the circulator pump to see if it is in the correct direction. This took me 6 visits to figure out the problem. I would never had found it but by chance the water temperature changed in the wrong direction. On the 6th service visit as I tested each zone individually... it was very clear what was happening.

Fontana

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EdTheHeaterMan said:

This is a shot in the dark but I had a noise problem years ago with a 4 zone (4 Circulators) system. One of the circulators was installed backwards during a repair. As it turned out if other zones were calling everything was fine. If the backwards zone was the only zone calling the water was reversed thru the boiler causing the water to return thru the supply and feed thru the return. The limit control was getting return water temperature when the water flowed backwards. The boiler overheated and the system had a banging like you could not imagine. Check the arrow on the circulator pump to see if it is in the correct direction. This took me 6 visits to figure out the problem. I would never had found it but by chance the water temperature changed in the wrong direction. On the 6th service visit as I tested each zone individually... it was very clear what was happening.

At least you kept looking till you found the problem..I think I have to find a real repairman, not just a service man..Would be nice to find an error like the pump in backwards but nothing has been changed since the original install...

nevele

You may be on the right track suspecting the circulator pump. If its not working the boiler temp will go up quicker than it normally would with one or more zones opened. You could try listening closely to the pump and slowly close off the isolation valve on the discharge side of the pump to squeeze off the flow of water. If you cant hear this happen the pump may not be working. Be sure not to leave it closed anymore than a second or so.

Fontana

nevele said:

You may be on the right track suspecting the circulator pump. If its not working the boiler temp will go up quicker than it normally would with one or more zones opened. You could try listening closely to the pump and slowly close off the isolation valve on the discharge side of the pump to squeeze off the flow of water. If you cant hear this happen the pump may not be working. Be sure not to leave it closed anymore than a second or so.

OK, I'll give it a go..Knocking usually starts at about half the temp rise [10° diff] towards high limit, hasn't mattered if high limit set at 170,175, or 180°..Thanks..Seb..

Fontana

Well here is an update..The knocking is still there but way subdued; last two winters have been some what milder [little snow] and while still some cold snaps down to near 0° constantly closer to 30's°..I am feeling that comments about the circular pump not having enough volume to handle if all four zones are open..A person told me that if I have a traco pump [I do] and depending what model it is I might be able to get a higher flow pump into existing housing..Doing car port now so will be next..