Boiler is short cycling

rickjames8

Hello,



I recently purchased a foreclosed house to rehab.  It was vacant about 10 months and during this time all the copper pipe was stolen including that for the boilers for the hot-water radiators.



I hired a contractor to replace all the missing pipes with PEX.  I haven't been thrilled with his work. 



He has gotten the old boiler to work, but it short cycles about every 5 minutes.  I've found the wiring diagram on line (Columbia MCB100) and it looks like its hooked up properly.  Also, it short cycles when the leads to the thermostat are joined. 



If does not look like he's created any sort of bypass system.  I see a feed line and a return line.   Could this be the most likely problem?



2 of the radiators are very cold, 2 are very hot and 3 are somewhere in between.   One of the medium ones is even hot on one side and not on the other.   Could this be due to the short-cycling or is that more likely a separate issue?



I know my contractor should be able to figure this out,  but I'm losing faith in him and can't afford to get someone else in to fix his work.



-Rick

Jean-David Beyer

Installation manal?

I am not a heating contractor. Is your contractor one who specializes in hydronic heating? Or a roofer who does plumbing on the side? If he does not know hydronic heating, the first thing to do is see if he followed the installation manual for the boiler you have. If not, it will have to be changed to follow the manual. This includes primary-secondary piping if required, connection of outdoor sensor if the boiler supports one, and so on. There are many other things that could be the problem, but that is probably the first thing to check.

kcopp

It could be a number.....

of things. The boiler could be oversized. If there are zone valves the anticipater on the tstat could be causing them to open and close the end switch. Or the operating control could be a bit wonky....

 

Mike Kusiak_2

Piped in series?

He didn't pipe the radiators in series did he? That would explain the different temperatures of the rads. It would also explain the short cycling if he piped them in series with 1/2" pex, as there is not enough flow to carry the heat from the boiler.



Each radiator should have a home run back to the boiler or a manifold. If he did not do this, then thats your problem

STEVEusaPA

Judging from your post....

Seems like your problem is either, lack of flow ( circs/ zone valves), or air bound heat emmiters, or a little bit of both.

Can you describe your system a with a little more detail? One pipe, 2 pipe, # of zones, zone valves, circs? How is it controlled? Post some pics.

Depending on how complicated the system is, it's possible it's piped wrong, or missing some components.

When you say 'short cycling' you seem to be describing 2 different scenarios--

1. Short run times- maybe the boiler is hitting its high limit, stopping for about 5 minutes, then restarting--which indicates a lack of flow (everything not getting hot).

2. Short cycles when thermostat calls for heat-- rapid on and off? Would indicate a wiring/thermostat issue.



All that repairing, you probably should've used a bypass, but Columbia only 'recommends' it as an option to protect from situations where low temperature water would return to the boiler.

Mark Eatherton

Get comfortable, you're going to be here for a while....

Got pictures of the near boiler piping system?



How about photos of the distribution piping?



Can you generate a simple piping schematic drawing?



Boiler information would be handy. House size is important too.



Generally speaking, we start with a heat loss calc, but in your case of existing conditions, it is what it is, and we will help you make it work as good as we can.



ME

rickjames8

Thanks for all the replies

@Jean-David

He is a general contractor who seemed to know more about plumbing than other areas.  I now have my doubts.   I have downloaded the manual and will give it to him tomorrow. 



@kcopp

The boiler worked in the house for many years according to the old tenants, so I think the size (70,000btu) is good. 



@others

The radiators are not in series.  There are no zones, they are all hooked up to the same line.   I've attached a basic diagram of how its hooked up.   Radiators 4&5 were getting the hottest.  6&7 were cold.  1 was mildly warm and 3 was warm on one side.  Rads with an * next to them are on the 3rd floor.   All others are second floor.   (This is a duplex, 1st floor is a separate system)



I think we may have found the problem today.   The circulator pump would come on initially, but after a couple cycles, it would not come on.   We tested the power going TO the pump and that seems to be active, so it looks like the pump is bad.  We're going to try a new one tomorrow.   The 2 rads which got the hottest were the ones located pretty much directly above the boiler.   So that might make sense.  It also might explain the short cycling, if the water inside the boiler got too hot too quick because it wouldn't cycle the cold water through. 



@Steve

I did read that columbia did not recommend a bypass for my type of set up.   Would you recommend putting one on anyway?  What are the advantages of that?



@all

Thanks so much for taking the time to give your suggestions.   This forum is a wonderful help.   I've given my contractor one more day to try to get this right before I call in someone else.   Again, thank you all so much.  I will let you know how the pump works tomorrow. 

Gordan

Can you mark up on the diagram

...what size tubing is where? Also, post a picture or two of how they're teed together. Is all of it PEX?



Looking at that diagram, I've got to say... it's not impossible that it could be gotten to work, but I'm not optimistic. That's not how one plumbs with PEX.

Mark Eatherton

Intermittent pump flow coud be a problem...

Your system is piped parallel direct return. (Here it comes Chris...) Water, is like my EX-brother in law. He was a water skiing bum. All he ever wanted to do was snag a ride behind a boat and go for another ride around the lake. Much like your heating system, he always like to take the path of least resistance. He was wet, lazy and stupid. (NOTE: As a part of always furthering myself, I have decided to take STUPID out of my syntax and replace it with something less offensive. I have decided instead to use the word dumb. It better defines him.) The water in your system just wants to get back to the pump (boat) for another ride around the lake (piping circuits). It (the water) too is wet, lazy and dumb, and MUST be shown where YOU want it to flow, because given the opportunity, it will follow the path of least resistance, which are those lakes (radiators) closest to the pump.



The "IDEAL" piping method would have been to pipe all radiators in a parallel reverse return fashion, which can still be done if piping is accessible. That way, all "paths" are equal, and subsequently, all flow will be equal through the radiators.



The alternative is to attempt to balance the flows by closing off those that flow well, and opening those up that flow poorly.



Another method is to install non electric thermostatic flow control valves on all radiators. This allows you to shut off unused rooms, and when open, once that room is satisfied, it takes itself out of the circulation loop, thereby allowing more flow to starving radiators.



Another point to make, and this is a common mistake, is that the use of PEX, while it is MUCH easier and faster than soldering, has some inherently high pressure drops through the piping circuit, requiring a pump of higher pressure generation capacity to overcome these inherent pressure drops. Each tee, each 90, even straight coupling have a relatively HIGH pressure drop compared to copper tubing. This can be seen by looking into the fittings used for these connections. They look real CHOKED... That will compound the imbalances that will already occur due to the direct return nature.



My EX-B.I.L., rest his soul, at least opened my eyes to the nature of nature :-) May he rest in peace.



ME

Ironman

Another Question

In addition to the good info that Mark has given about your piping, let me ask another question about your system: Did your "plumber" use oxygen barrier pex or regular plumbing pex which is only designed for potable water? If he used regular, non-barrier pex, then you're gonna have all kinds of issues including a very pre-mature boiler failure.



O2 barrier pex is required and is clearly labeled.



Also, can you show you line sizes and their lengths? What make and model pump? where is the pump located?

rickjames8

Will get more info tomorrow.

The house that all of this work is going in to is not where I am presently living.  It's about 15 minutes away.  I can find out pipe size and PEX type tomorrow.   All the heating PEX looks larger than the potable water PEX.  The pumps are physically attached to the boilers. 



I had actually thought about the path length when looking at the system, realizing that the ones with longer travel would probably have more trouble getting hot water to them.  I just assumed this was fixed by adjusting the valve at the base of each radiator.  (Again, this is my first experience with hot water heat)  Although one of the hottest rads was one the furthest away.  But, as Mark pointed out, I think it may have had the least 90's and couplings.



As for the PEX type, the lines used for the heater do look clearly different.  I've attached a photo (one I took weeks ago to document the rehab).  Red/blue are hot/cold potable, and white is heating - both feed and return.   I have noticed that in some places it looks like he may have used a small piece of blue pipe here and there (perhaps ran out of the white stuff??)   There is a fair bit of copper pipe he's reinstalled.  Most of it is near the boiler itself, and the rest is where the PEX meets the old pipes. 



The system does seem to work now in the upper apartment, the new pump seeming to have done the trick.   The lower apartment system worked well this morning,  but seems to have shut off now.   But I'd like to make sure it's done right if there is a chance it could damage the heating system if it's hooked up wrong. 



I will take more photos tomorrow along with whatever markings I can find on the pipes. 



@Mark - can you point me to a link/image showing the difference in parallel direct and parallel reverse?   I googled it and came right back here to hh.com, to some good threads, but still none which really helped me grasp the difference. 



Thanks again for all the help.  I'll try to get on the internet mid-day tomorrow with more info. 

Mark Eatherton

Parallels.

See attachments.



ME

bill_105

Just curious

Are you in PA?

rickjames8

So, something like this?

Thanks for the images.  Exactly what I needed to see.



Would this image be a better way to hook it up?

Mark Eatherton

In a word,No....

You are still set up direct return. All you've done is to separate the system into two direct return loops, as though you were going to have two separate zones.



Think of the flow (in your perspective/case) as going around in a large circle. The supply and the return MUST both flow in the same direction as the water works its way around the circle. Once all radiators have been picked up, the final revere return head back to the boiler for more heat and more push from the pump.



One thing I neglected to mention is that the pressure drop through each radiator/heat emitter must be approximately the same, or the Lazy Bro In Law syndrome will still come back to bite you (imbalanced flows).



As your supply pipe starts out full size, it can and should decrease in size as you drop branches at the heat emitters. The return will start out at the first radiator small, and increase in size commensurate with the decreases in size on the supply main. At the heat source, both pipes would be the same size.



Size is based on connected flow. In order to determined connected flow, you would need to calculate the EDR or BTUH capacity of the attached loads/heat emitters.



Reverse return piping WILL chew up more pipe and more time, but it is self balancing, and provides the ultimate in comfort. ALl emitters get access to the hottest available water at nearly the same time.



You can also install non electric TRV's at the individual radiators (except the one that the thermostat for the house references) and get individual control for all rooms. You could do the same with a direct return system, but at design conditions (all valves wide open) you'd still have balance issues, whereas with the reverse return system, you'd be good to go.



Another picture I can paint in your mind is to look at an upright extension ladder. Assume the heat source is in the basement (bottom of the ladder) The rungs are the emitters. Water flows up the right leg of the ladder, across the emitters (rungs) and down the left leg of the ladder. Direct return means the water in the supply leg goes up, and in the return leg flows down.



Now, cut the lower left leg, and the upper right hand legs off of the ladder. Go up to the upper left hand side of the ladder, and connect a pipe to the top left hand side of the ladder, and run it back down to the basement. Now, as the supply water flows up, the return water flows in the same direction (up) until it gets to the very top of the ladder, where it turns 180 degrees (reverse return) and the return water then flows down, back to the heat source and pump.



So to recap, in a direct return system, the return flows in the opposite direction of the flow as it goes past the rungs (emitters) of the ladder.



Reverse return has the supply and the return flowing in the same direction until all rungs have been hit, and then returns in the opposite direction back to the heat source.



I will have to switch machines to make you a drawing to show you how to ideally pipe your system.



Did you want one zone, or two?



ME

Mark Eatherton

single zone drawing

attached.

Mark Eatherton

2 zone drawing

More pipe, valves and fittings.

rickjames8

Sorry for the delay

I've been staying at the property and there is no internet access there and we've had a lot of other 'little emergencies' come up.



The heating system seems to be working now, but I still think there were errors that need to be addressed. 



I've attached 3 photos (files lars1-3.jpg) of the new boiler install.  Not sure if that helps at all.  It looks as though it does have a bypass.  As you can see, the feed pipe has a short (3-4 feet long) piece of smaller diameter blue pipe which I would think is choking the system. 



Also, the white sharkbite PEX used for the heating system is rated for 180F@100psi.  The guy at Home Depot said that they usually recommend the orange PEX for heating installs, but they seem to have the same temperature rating.   However, one of the pipes has begun to sag due to the heat.   It feels rubbery like garden hose.   I've since learned that it should have supports on EACH joist, which it obviously does not. 



There is also a photo of the old heater install (this one has no bypass). 



Given that the heating system is working ok now, would you still recommend re-piping it to the parallel reverse return, given that it would be a considerable job? 



Mark, I must say thank you for your generosity of offering advice on this forum.  It's been an amazing help.   If you're anywhere near the Philadelphia area, I'd love to buy you a beer. 

Ironman

Non-Barrier Pex

That 's non-barrier pex that was installed on your system. The temp rating is not the issue. Non-barrier pex does not have an oxygen diffusion barrier. Simply put, that means the pipe you have will absorb oxygen into the system which will cause your cast iron boiler to rust out and fail along with a host of other secondary issues.



Your piping is a cob-job done by a hack that was unqualified. I feel for you, honestly. We see this kind of thing all too often.



Unfortunately, it's all got to be done over by someone who knows what the're doing or you'll soon be replacing the boiler(s). It looks like you have 2 boilers?



I would highly recommend that you contact a "pro" right away. Check the "Find a Contractor" tab above.

rickjames8

Thanks.

Wow - thats hard news to swallow.   Is oxygen-barrier PEX more expensive?  I'm trying to figure out why he may have used it.



Also, on an unrelated note, we have a radiator upstairs which only has one working fin - it happens to be the fin which has the bleeder on it and the fins are only internally connected at the bottom.   How do I get the air out of the other fins?



There are no contractors listed on HH.com near Philly.   Closest is in Reading.   I have much more confidence in the contractor coming over this week. 



We have our life savings in this house.  We were (are) on an amazingly tight budget and went with a GC we thought knew what he was doing.   In the end, it looks like we made a big mistake choosing him and it will cost us so much more in the end.   Lesson learned the hard way.   From now on use HVAC specialists for HVAC work. 



-Rick

Ironman

I'm Sorry...

To be the barer of bad news.



Try starting a new post entitled: "Looking for a Pro near Philly". There are regulars on this site who are near you.



Simply choosing an HVAC contractor does not mean you'll get a hydronics Pro. Most know little about hydronics. Get some references from customers who have hydronic systems before choosing a contractor.



The most likely reason that your G.C. used non-barrier pex is that he wandered into an area where he had little or no expertise. So many people that aren't wet-heads think that a boiler is just like a water heater: just hook up two lines, turn on the gas and walk away. That isn't true in either case, especially hydronics.



Regarding the rad that only heats on one column: it sounds like it's a steam only rad. There's no way to get the air out of the other columns.



Stick around and keep asking question here. You'll get help.

bob eck

contractors near Philadelphis

How close are you to Philly. I work for a Plumbing & Heating wholesaler in Allentown and I have customers in Bucks county that could help you.

Yes radiant pex tubing with oxygen barrier is more expensive than regular pex pipe. Look at using Viega fostapex pipe with aluminum with oxygen barrier. this tubing will not droop or grow when running hot boiler water through it radiant pex will droop and grow when running hot boiler water through it. The hotter water the more the regular radiant pex will droop and grow.

why don't you us a radiant header like the ones from Ledgend Hydronics and run 1/2" pex direct to each baseboard or radiator in each room. you could balance the system real easy that way. I the future you could go to a condensing gas boiler and the piping would already be done.

Send me a email as to where your house is.

Good luck

Mark Eatherton

Oy....

It looks like it was installed by a less than skilled person.



If it were me, I'd repipe it t make it more reliable and dependable. Nothing worse than worrying about your heating system when you're not there.



Non barrier PEX is a huge issue. It can be addressed by maintain a high pH, but requires checking on a regular basis, and when things go to hell in a a hand basket, it happens quick, and in your case a WHOLE bunch of components will be affected (basically anything ferrous is going to go away). Alternately, you could set a brazed plate heat exchanger to isolate the boiler from the rest of the distribution system,... Scratch that idea. You've still got ferrous components in the field... Sorry for the false hope. Maintaining pH is still a viable option but you will eventually forget to do it and then everything crashes.



With this much ferrous stuff in the system, I'd really strongly recommend you replace the non barrier pipe with barrier pipe. That is the BEST long term solution. And as Bob Eck pointed out, maybe the use of a central manifold with 1/2" or even 5/8" BARRIER PEX to the rad's would be a better option for a DIY type of person. It requires less piping skills, and can be done in less time than doing the parallel reverse return system, and it too would provide the same water temperatures to the rad's when they call.



While you are at it, you need air separation/elimination, and that expansion tank shouldn't be hanging in mid air as it is without substantial pipe support. If it snaps off, and you're not home, you could come home to a swimming pool in your basement, At that point, the code REQUIRES the appliances to be replaced.



Sorry we didn't have better news for you, but if you ignore this system, it WILL be very problematic for you...



PEX does get soft, and absorbs more O2 when its hot, and it also expands in length a great deal.



Can you take a picture of the problematic radiator? Could just be air bound. You NEVER want to bleed a standing radiator system with the pump ON. Maintain adequate water pressure to push air out, but do not try and bleed with the pumps running. You will miss a WHOLE bunch of air.



FWIW, you could probably go thru this winter without dong much damage to the system so you're not replacing a heating system in the middle of the Winter. Just turn the water temperatures as low as possible (~ 150 F?) to avoid oxygen diffusion.



I'm in Denver, a long ways away from Philly



Thanks for the offer anyway.



Get back to us on the troublesome radiator.



The fact that your system corrected itself indicates to me an air problem, but that is a blind recommendation. (air got pushed to and is trapped in the upright radiators)



ME

rickjames8

Address

Bob - I am not far from Bucks.  My zip is 19401 (Norristown - its outside of Philly). 



Re the rads:  I figured out in the middle of the night that they were steam radiators - one of those things that just dawns on you at a random time.   Not sure why they're tied in to this system.  It looks like they've been there for a while. 

bob eck

boiler is short cycling

look on craigs list put in Philadelphis area there are a lot of used radiators on there for sale. Just dont get steam radiators.

Mark Eatherton

Some steam radiators can be used with hydronics...

SHould be completely connected across the top, and will need some means of venting the air out of the top of the radiators, assuming it is double tapped on the bottom of the radiators.



Take pictures the next time you are on site.



ME