Combi-boiler, cold rooms and two types of radiators

aw273

Hi All,

I've searched around the forum and didn't see a similar situation, but I've tried to read through the overlapping components that are relevant. I hope you don't mind me trying to get some more specific advice.

We have had a Navien combi (the 240 size) for six years for our radiators and for domestic hot water. the House is in the Toronto, Ontario area and was built in the 50s with dual brick/no insulation. We haven't done any changes other than changing the boiler, the radiators and pipes were all in place when we bought the home, more than 15 years ago.

We have two types of radiators, which I see on the site is not great, but they were in place before we got there. We have 2 cast iron and 10 that I think are brass tube/copper fin? (they are covered in steel boxes with the vents on the front side, near the top, that remind me of my old elementary school).

Our upstairs is generally uncomfortably cold, even though the fins on the radiators get hot.

That's the background, but not the main reason I'm writing. The issue is that in six years, we've had a number of problems with the domestic hot water and a leaking pressure release valve. Every 6-9 months, it seems that the domestic hot water starts to oscillate (shower gets hot and cold while you're in it), without any error codes on the boiler; we're pretty sure that it is the mixing valve that needs to be replaced for the second time. And in two years, we've had to replace the pressure release valve twice due to leaking.

Our latest service person said that this is all probably due to gunk in the radiator systems (rust, etc.) and it causes the pressure relieve valve to be damaged and stuck open/dripping. So they suggested removing all of the radiators and pressure washing them to clean them out. But this would have nothing to do with domestic/mixing valve, so not sure if that makes sense.

They also suggested that the cold upstairs is likely due to the radiators being bipassed (again, the gunk in the system), and they showed me that the returning water pipe is almost as hot as the outgoing pipe. But I actually think this might be due to the inefficiency of the brass tube radiators.

One place said try Fernox, but the others said that won't help. . .

And finally, as I've spoken to potential companies about "cleaning the rads" most of them have said it would be better to replace the brass tube radiators with stelrads instead of trying to clean them and put them back, but I've heard different advice about having stelrads and cast iron on the same loop, too.

So, in short:
1) why does my mixing valve keep failing?
2) why does my pressure relieve valve keep failing?
3) are they in any way related?
4) should I try Fernox (it was an expensive service, but less than replacing rads)?
5) would it make sense to change some of my radiators to stelrads (in the coldest rooms)?
6) does changing any rads only make sense if I change all the brass radiators at once?
7) does changing radiators only make sense if I change all of the cast iron and brass tube ones to a new type?


Thanks for your help, and I hope most of this makes sense

aron

Jamie Hall

Well... it does, but we will need to know more.

First, is there an expansion tank on the domestic hot water? Is there one on the heating system? There should be...

Second, is there a pressure gauge on the heating circuit? If so, what does it show when the heat is off? What does it show when the system is nice and warm?

Third, and most important -- there's nothing wrong with copper fin convectors, though I dare say that a good flush might well be in order. And there's nothing wrong with cast iron radiators But... they don't play well together. Are they piped so there is just one zone? Are they piped so the water goes from one to the next to the next and so on, or are they piped so that they all work off one main pipe and return to another? Ideally the upstairs radiators would be one zone, with its own thermostat, and the cast iron ones would be another zone, with a different thermostat.

Ironman

First, you need to find a competent HYDRONIC tech; your current one is clueless.
Second, a bad 3 way valve won't cause over pressurization.
Third, sludge in the system (if it's there), won't cause the relief valve to leak. The relief valve is leaking because the system pressure is too high. That's probably due to an under-sized expansion tank or a bad or misadjusted fill valve.
Forth, if there is sludge in the system, you remove it by flushing and using treatment such as Fernnox, not removing the radiators.

We really need some pics of the boiler with its near piping, the pumps, controls, piping arrangement and the rad's.

aw273

Hi Jamie and Ironman, thanks for replying

there is one expansion tank, which I believe is on the heating circuit.

I don't know how the pipes run, like I said, they've been there for 60+ years, but there is only one zone and only one thermostat, so unfortunately the upstairs and downstairs and the copper and the cast iron are all combined.

The Combi has a pressure gauge readout that alternates with the temperature. If I recall correctly, it normally averages 180F and 31psi, but I'll have to double check at home.

I have a picture of the boiler, but it doesn't show the small pump that's connected to the pipes in the basement ceiling.


i

aw273

and here is one of our bedroom radiators. we have 10 of these in bedrooms, kitchen, living room, and dining room.

The last two radiators are a small cast iron one in the bathroom and a wall mounted cast iron one in the basement

SuperTech

Boiler pressure should never be near 30 PSI!! The pressure relief valve is opening because it's supposed to open up at 30 PSI. Your expansion tank is likely undersized and most likely the bladder has failed. A high mass system like that probably needs a #60 or larger expansion tank.

I agree with the above statement about your tech being clueless. I've never heard of such a load of b.s in my life. Sludge in the system and removing radiators to power wash them...SMH.

Maybe try the find a contractor tool on this site, perhaps you could find someone who has a clue about hydronics.

aw273

I might be incorrect on the pressure, but I can check at home. I know for sure that the pressure didn't change between the relief valve not dripping and dripping - and I've had two different companies (one this time, one a few years ago) tell me they need to be changed out because they've failed.

The good news is the current tech is not trying to sell me anything. . . he's just making expensive recommendations

The expansion tank is definitely being replaced though - not sure of the size, I can check that too at home.

But, I'm still getting a mix of opinions from the hydronics companies I've contacted (, Fernox, all new rads, some new rads, etc.).

And I'm still confused if sludge might be keeping the upstairs from being warm enough, or if it's the mix of radiators, or something else.

also, the domestic side issues on the mixing valve (which are probably entirely unrelated to everything on the heating side)

Jamie Hall

Well, I'm glad the expansion tank will be replaced. I hope whoever does it does it right. Your pressure on the heating side shouldn't be over 18 to 20 pounds hot, and should be about 15 pounds cold.

You don't need new radiators. You do need to flush and purge the system. You don't need Fernox to do that, though it wouldn't hurt.

And it's unlikely to be sludge causing the problem upstairs. Much more likely is that the flow is pretty well bypassing the radiators -- and the reason for that will depend on how the system is piped. To determine the reason -- and therefore the fix -- you need an man or woman quite experienced in hot water heating systems to take a look at how the system is pumped and piped, and figure out how to balance it.

Hopefully the domestic hot water is completely isolated from the heating system. So the mixing valve problems are unrelated to the heating problems.

aw273

Thanks Jamie.

we've had a number of different companies through, but no solutions so far.

yes, the domestic is completely separate, but still frustrating.

and SuperTech, I did try the contractor tool, but it seems like it is US only, and I'm in Canada.

aron

SuperTech

That's unfortunate Aron. Keep researching different contractors and if you need any second opinions on their recommendations the advice you will get here is free. Expansion tanks are sized according to the volume of water in the system. Typically a #30 tank like you have in your picture isn't adequate for most systems with large pipes and cast iron radiators that hold a lot of water. It's possible that your tank is adequate but has failed, that would explain the relief valve issue. Tap up and down along the side of the tank. If it's ok you should be able to tell where the water is and the air blader is by the hollow or solid sound while tapping it.

Jamie Hall

Yes, the site is short on folks in Canada -- there's no restriction on they're being here, they just don't seem to be.

Is it possible that you could draw a diagram of the system, showing where the pipes go and connections to radiators and all the valves and pumps and other bits and pieces? And the boiler? It doesn't have to be a draughtsman's masterpiece. It would help, though in visualizing what you have and what might be done about it.

Ironman

How many square feet is your house and where in Canada are you located?

aw273

Thanks All,

we are in Toronto. the house is 1950's vintage, two stories with a finished basement.

There are 12 radiators, 10 brass tube and 2 cast iron. Unfortunately, I'm not sure how to know how the pipes would travel from radiator to radiator to draw a diagram. . .

the Expansion tank has definitely failed, which probably caused the dripping valve and high pressure. so hopefully that will get fixed with it being replaced.

But going back to my initial seven questions, I'm confused why the domestic side mixing valve keeps failing and about the various recommendations for changing some or all of the radiators to try and make the top floor more comfortable.
- if the current mix of radiators on one loop is "bad" than won't a new mix of radiators also be "Bad" or worse?

thanks again

aron

Jamie Hall

Changing radiators just isn't going to help. What will help is two things: making sure there is no air or sludge in the upper floor radiators, and balancing the flow between those radiators and the others.

To do that you are going to have to do some sleuthing, I expect. What I would do is start at the boiler outlet, and start drawing lines representing pipes. Be sure to draw in -- in the correct relative positions -- any fittings other than elbows (you don't have to worry about elbows!). When you get to a pump, try to figure out which way the water is flowing through it and make a nice arrow. (Yeah, I know it sounds dumb, but I still have been known to do this sort of thing, 50 years on!). What you are trying to do is figure out how the water gets around the system. If something disappears into a wall, make a notation. If this doesn't get you all the way back around to the boiler inlet, start doing the same thing working back from the inlet.

Frankly, what I'm hoping is that somewhere in there you will find a pipe or pipes which clearly goes upstairs -- to that top floor -- and others which clearly feed the radiators downstairs. If you are really lucky, you might even have valves on those lines...

Post what you get. Don't worry if it isn't finished. See what we can do with it.

aw273

For balancing, all of the valves on the radiators are frozen solid, because i wanted to try and restrict the main floor, but couldn't.

Thanks, I think I get what you're looking for, but my hesitation is that other than the laundry room where the boiler is, the basement and house is completely finished. So how do I tell if radiator 1 is connected to radiator 2, or vice-versa?

So I could map the one room, (it has a drop ceiling, so even that is a bit harder than if it was open, but doable), but once it goes into the drywall, how do I know where the pipes go?

thanks,
aron

Jamie Hall

You don't, really. But you may be able to make some guesses -- where might the pipe go? Is this bit of pipe on this wall getting hot? Find a radiator which gets hot not much later. That sort of thing... don't give up!

Ironman

Your square footage is needed to estimate your total heat load. It doesn't have to be exact, just close.

I'm definitely going somewhere with this, but I don't wanna run you down that trail until I can be sure.

aw273

approximately 2000 square feet on three levels (basement, main and upper floor). House is a 1950's center hall plan that is 20'x30' floor plates, with a small kitchen extension. So that is 600 sqft on each level, plus maybe 200sqft added on to the kitchen on a pier foundation (so no basement or enclosed crawlspace under the extension)

Ironman

Do you know what Supply Water Temp the boiler is set to? Is the Out Door Reset feature operational?

aw273

No sure about the supply water temp and I don't know what an out door reset feature is. . . sorry

I know there is an external temperature sensor on the exterior of the house, if that is at all relevant

Ironman

That sensor is for the ODR function in the boiler. It adjusts the SWT based on outdoor temp. The colder it gets outside, the warmer the SWT to the rad's and vise versa. It's an adjustable curve which may be needs tweaking.

The convectors that you have require a much higher SWT than the cast iron rads. The ODR curve needs to be properly set to deliver a hot enough SWT for the convectors.

Forget about the SWT to the rads; you can install Thermostatic Radiator Valves on the cast iron rads if needed to control their output.

I suspect that this is your main issue, not sludge that's restricting flow.

aw273

Ah, I know the heating water temp was maxed out at 180F. Fortunately, the CI rads are both covered. Currently, they don’t have thermostatic valves on them

aw273

ok, this is terrible, I'm sorry. . .

the empty white box is the boiler, and you can see the pipes in close proximity in the real picture, above.



basically, there is one pair of big pipes (hot and return) that goes into the wall towards the front of the house and one big pair of pipes that run across the house near the back. They each have branches that I assume either go to radiators or to the second floor, but I don't know which would be which. none of them would line up directly with a radiator above.

Ironman

When you say "big pipes", are they iron or copper? What's the approximate diameter?

aw273

Pipes are all iron, except the new ones at the boiler.

The “big pipes” are all iron and are the main runs off of which smaller pipes branch.

The initial iron pipes are 2” diameter, and the branches are probably 1” or 3/4”

At the radiators, the pipes coming in and out are also about 1” diameter

Ironman

What's the pressure on the boiler gauge when it's cold? What when hot?

aw273

With the caveat that the expansion tank is being replaced tomorrow, it was 17 psi with the heat off before, and 32 psi heating now

Jamie Hall

I think you mentioned somewhere up there, @aw273 , that the return pipe(s) from the misbehaving baseboards were hot. Are the returns from the cast iron radiators also hot? If not... you may be able to figure out which sets of pipes go to the baseboard(s) and which to the cast iron by feeling the returns.

Ironman

aw273 said:

With the caveat that the expansion tank is being replaced tomorrow, it was 17 psi with the heat off before, and 32 psi heating now

With large pipes and convectors, you need a larger expansion tank than an Exrtol 30. I'd put at least a 60 or 90 on there.

The small tank (30) is what's causing your pressure to get too high. There's not enough volume in that small tank to accept the expansion of the amount of water in your system when it's heated.

aw273

Hi Jamie,

There are only 2 cast iron radiators in the house. One is easy to identify, it is on a wall in the bedroom in the basement, and I marked it (poorly) on the diagram at the end of one set of large pipes.

The second CI rad is in the front of the house, on the second story in the bathroom. I checked, and there is a difference in the temperature between the "in" and "return, but none of the pipes in the laundry room ceiling have a differential that I can feel.

Since the radiator is in the front of the house, I would actually guess the pipes to it are much later in the run that leads off through the laundry room wall and into the finished ceiling in the rest of the bedroom.

aw273

Thanks Ironman,

I'll talk to the tech about that today. This repair is covered by a warranty, and I assume they are going to install an exact replacement, but I can see about replacing it/upsizing it today or separately.

aron

ChicagoCooperator

Have you taken the covers off the convectors and cleaned the actual fin tube elements? Years of dust will really block the air flow. Also, if you have dampers on the covers, make sure those are open too.

aw273

thanks ChicagoCooperator, the guy who just came through suggested I clean the convectors too. will do that very shortly!

Paul Pollets

I agree with Ironman, a 60g expansion tank would be preferred. The system temperatures are controlled by the ODR and it needs to be setup correctly. It's likely the heating curve needs to be raised. The near-boiler piping to the system should have a thermometer downstream from the pump and a purge port on the return.

aw273

Unfortunately, I can't get the covers off the convectors. they are all painted shut and buried in the hardwood flooring. I think I'd need an angle grinder (which I don't own) and a lot more skill than I have, to get them open without damaging the floors or the pipes.

ChicagoCooperator

Utility knife to score the paint! The cover should lift off (it looks like my old living room convector), more or less straight up.

aw273

I did score the paint, and broke more paint, but I think there is a lip at the top of the panel that fits into the top of the convector body. So it needs to come out from the bottom and down, I think?

Brewbeer

Can you post a photo? If the bottom of the baseboards are too close to the flooring, that will restrict their output.

aw273

Hi Brewbeer, there's a photo above - there is about 4 inches to be bottom of the fins. it is just the bottom 1/2 inch or so of the front panel is buried in the carpet and/or hardwood underneath and so I can't get the panel off.

aw273

couple of updates:

1) same expansion tank was replaced on Thursday.
- the Tech tells me it is the correct size for the system.
- The system pressure seems to be at about 25psi.
- I know a couple of people on here have said it shouldn't be above 20psi

2) I see evidence of dripping from the pressure release valve again today.
- I don't know if the pressure went above 30psi and so triggered the valve, or if something else is wrong.

3) separately, two different potential companies want to switch some or all of my brass tube radiators to Stelrad or cast iron (to fix the heat/comfort issues, not the leaking issues)

Ironman

aw273 said:

couple of updates:

1) same expansion tank was replaced on Thursday.
- the Tech tells me it is the correct size for the system.
- The system pressure seems to be at about 25psi.
- I know a couple of people on here have said it shouldn't be above 20psi

2) I see evidence of dripping from the pressure release valve again today.
- I don't know if the pressure went above 30psi and so triggered the valve, or if something else is wrong.

"The tech tells me it's the right size."

But several pro's, with hundreds of years of combined experience, tell you it's not. And you have the exact same issue that you had before.

Amtrol has an online sizing tool, but you've got to use the commercial calculator because of the size of the old gravity pipes.