Stelrad Panel Radiator not getting Hot.

skiereric

I have a large system. 26 rads in total, however, I am only having a problem with one radiator (located on the ground floor). The radiator is getting some heat, but I would say is 5% of the other rads in the house.

It is a Stelrad K1 panel installed in 2000.
Connected with Pex with separate return and supply lines controlled by a manifold
The return/supply valve manifold is fully open
I can feel heat in the supply line
The return line is cold
I am able to bleed the radiator
I have taken the radiator off the wall and flushed it clean
The lock shields are fully open.

Any ideas on how to fix or continue troubleshoot?

Jamie Hall

Clearly it is starved of flow. The question is, why? It is worth remembering that water is lazy, and will always take the path of least resistance. Therefore, if you have eliminated all possible sources of extra resistance in the circuit to that radiator, you need to look further back in the system and find out what other paths the water can take which have significantly less resistance -- and slow them down.

But first be really sure that you have checked all the possible restrictions to flow for that particular radiator. If this is a new problem -- not one since the first install -- the very first thing to do is to go back over any changes, however, irrelevant they may seem, to the system which may have been done around the time you noticed the problem.

Ironman

How about some pics of the other rads and the system piping? Also, the boiler and its near piping?

skiereric

I am going to isolate that section using my manifold valves to see if the increased pressure will help at all. It's a one pump set up.


Is there any risk of this?

skiereric

Jamie Hall said:

the very first thing to do is to go back over any changes, however, irrelevant they may seem, to the system which may have been done around the time you noticed the problem.

I have lived in the home for 1 year, and I have always had this problem.

Ironman

How about a pic of the pump? I seriously doubt that it’s sized or designed correctly.

skiereric

Ironman said:

How about a pic of the pump? I seriously doubt that it’s sized or designed correctly.

Here is the pump - it is on the return side.

skiereric

Ironman

Try turning the pump to the highest speed.

skiereric

As you can see the pex is quite dirty. I don't think inhibitor was ever used. I had a Magnetic Filter installed yesterday and added some system cleaner to it to see if it might help dissolve some potential blockages in the pex/rads.

skiereric

Ironman said:

Try turning the pump to the highest speed.

Just checked - it is already at it's highest setting "Hi"

Ironman

A manifold with 16 loops that’s piped direct return is a ridiculously poor design. 26 loops on one pump with 3/4” lines is also as bad.

Whoever did this had little or no knowledge of proper hydronic design.

It’s  probably never gonna work right unless  the manifolds, piping and pumps are redone correctly.

skiereric

Ironman said:

A manifold with 16 loops that’s piped direct return is a ridiculously poor design. 26 loops on one pump with 3/4” lines is also as bad.

Whoever did this had little or no knowledge of proper hydronic design.

It’s  probably never gonna work right unless  the manifolds, piping and pumps are redone correctly.

Yup - previous homeowners obviously hired the wrong guy. I am planning a top floor reno in the next 12 months, and will add a budget to tackle a redesign then....any idea on a rough cost to redo this?

It is just strange that 25 of the 26 work fine. Just that one radiator. I was hoping it could be a poor flow/blockage in the return pex or perhaps a end of life radiator.

Ironman

Talking price is against site rules. The best I can suggest is find a good, competent hydronic/radiant contractor, not your everyday plumber or HVAC guy.

Try the contractor locator above.

One of the biggest issues is that extremely long manifold that’s piped direct return. That means that the last loop fed is also the last returned. It’s gonna get the least flow. The loop itself could also be the longest.

Whenever I have a manifold with more than six loops, I pipe it reverse return, meaning the first loop supplied is the last returned and vise versa. This provides equal flow to each loop.

You may get more flow to the last loop by throttling down (not closing) the flow setters to the other loops.

Jon_blaney

Have you checked the manifold valves. My guess is that one of them is stuck closed.

Jon_blaney

Did you bleed air from the radiator?

skiereric

Jon_blaney said:

Have you checked the manifold valves. My guess is that one of them is stuck closed.

Yes, however without a built in flow meter, I am just guessing if it's working. The return pex below the valve on the in question manifold is cold.

I have ordered a replacement cartridge to test if its broken.

skiereric

Jon_blaney said:

Did you bleed air from the radiator?

Of course! No air, only water.

jumper

Can it be that somehow flow is too "laminar"? Try slowing pump down. Then do good rads become cooler? Does the room with cold rad have a high heat load? Usually there's always sufficient supply when there's a circulator moving water.

First suspect is the panel itself. Anyone ever come across a defective one? I wouldn't like to switch a couple to find out but that is obvious thing to try if you strongly desire to fix problem. Lazy guy like me would just buy a space heater.

skiereric

Follow up to this post. Using the radiator valves/TRVs, I shut all the other radiators on the same manifold off.

After a few minutes, I was able to get the trouble radiator hot, albeit with a few spotty warm spots.

I then reopened the closed radiator valves, but unfortunately, the troubled radiator failed to stay hot.

Any idea what this means?

Jamie Hall

Backing up a moment. You closed all the other valves so that the only place hot water could go was to this problem child? And it got hot, at least mostly.

Then you opened a bunch of other valves and it got cold again, or let's say it cooled off.

OK. Not rocket science here. Water is lazy. Very lazy. And it will quite cheerfully flow most in circuits which have the least resistance -- and much less in circuits which have more. I am going out on a limb -- but only a very small way -- to suggest that the problem is that the circuit which feeds the problem child -- including the radiator itself -- has much higher resistance to flow than the other circuits. To pin this down, you -- or we -- need to analyse exactly what fittings and valves are in each circuit, and the flow resistance of the radiator itself, to see what is happening.

I don't suppose that you had any way of recording the pressure gain across the circulator pump when just that one radiator was on line, and compare it to when they are all open?

neilc

is there any harm in throttling all the other loops ?

close em all down 50%, except for the cold one,
got flow to cold rad now ? good,
then if another loop is too cold, open it a turn,
and if one stands out as too hot, close a turn,

if you reach a balance, try opening each a bit, 1/4 ~ 1/2 turn, until cold rad acts up again,
this could take several attempts / days

skiereric

In the recent cold snap, I was able to spend some time balancing the manifold with some success, but still room for improvements.

Some finding and questions.
For my two trouble rads, the supply lockshield valve is hot, the rad is lukewarm and the return lockshield is cold (I have confirmed that the lockshield are fully open).

Since these rads are the furthest side of the house from the boiler I expect I have weak pressure (the circulator is on the return side). I seem to have improved flow through the rad when closing the return lockshield - would Bernoulli's theorem apply here - pressure increasing as i decrease the opening of the valve?

On the coldest days, the rad behaves better (warm) and on cold days it is lukewarm. So again, back to increased pressure, I assume with the hotter water.

I am curious to try to isolate the section of the manifold so increase the pressure to see if it will help push obstructions out of the way. The manifold has three sections with shut off valves for each section of supply and return.

Any risk of causing any problems by shutting down the other sections?

Paul Pollets

Move the pump to the supply, pumping away from the expansion tank and I'd bet the problem goes away. When you're using TRV's the manifold port should be fully open; any adjustment is done with the TRV.

Jamie Hall

If you have a manifold, the pressure on all the outlets (or inlets) is going to be almost exactly the same. It will drop as the flow goes through a valve; a fully open valve, very little. A partly open valve, a lot. And t is pressure differential between one end of a pipe -- or radiator -- which causes flow.

Bernoulli's theorem has nothing to do with it. Any pressure loss from the increased velocity going through the valve is immediately recovered on the other side; any pressure change is due to friction losses in the valve.

ScottSecor

@skiereric I just noticed that you were able to induce flow when you bled this troublesome radiator for an extended period. This tells us that the radiator valve is not clogged and the unit is not clogged. I think, like others suggested your piping. As Dan has taught us and @Paul Pollets suggested above, "pump away" (and improve the piping) and I think EVERY radiator will produce more heat.

skiereric

I found the original engineering design from pulling a disclosure on the building permit from 2002. Although it does not look like they followed it to a tee. For example, the design had the circulator pumping away from the expansion tank. but in reality, it is pumping towards it.

Ironman

The pressure bypass valve may be letting too much bypass.

Paul Pollets

I'd replace P2 with a Grundfos Alpha smart pump and remove the bypass.

skiereric

I believe I have figured out the issue.

The original installer used two return lockshield valves on the same radiator. I expect this is why a little bit of flow occurred but not enough to truly heat the radiator.

These are the valves that are currently installed. https://www.herzvalves.com/catalog.php?prodID=233&lng=gbr

I plan to swap the return valve that was installed on the supply side with a Thermostatic valve.

mattmia2

skiereric said:

I am going to isolate that section using my manifold valves to see if the increased pressure will help at all. It's a one pump set up.


Is there any risk of this?

oh my

skiereric

oh my

I know. I know. It's ugly. Plastic manifold from the early 2000s. One circulator. For four floors and 26 heat emitters.

It's going to be a big job to redo this distribution system.

This summer I am going to be installing TRVs on all rads and replacing the circulator with a smart one, and rewiring for constant circulation. And also trying to flush it clean so the pex doesn't look brown anymore.

mattmia2

Did you take a good look in the 2 radiator valves to see if there is debris in the valve or where the pex connects to it or if the seal from the valve came loose and is floating around inside? You can also swap 2 connections to the manifolds to see if it is something clogged in the manifold.

The diagram looks like it shows primary-secondary pumping, is it actually piped that way?

GGross

What size pipe is hooked to your circulator?

As others have said, 16 loops on that manifold is a bit much, you can see at least one repaired piece of pex and it's not installed neatly, which makes me wonder what the pex buried in walls etc is up to.

mattmia2

GGross said:

What size pipe is hooked to your circulator?

As others have said, 16 loops on that manifold is a bit much, you can see at least one repaired piece of pex and it's not installed neatly, which makes me wonder what the pex buried in walls etc is up to.

or it is kinked somewhere

skiereric

GGross said:

What size pipe is hooked to your circulator?

As others have said, 16 loops on that manifold is a bit much, you can see at least one repaired piece of pex and it's not installed neatly, which makes me wonder what the pex buried in walls etc is up to.

It's 1 1/4, which then reduces in size at each section of the manifold to a final size of 3/4 inch for the top floor.

skiereric

or it is kinked somewhere

I am a bit afraid to remove the pex from the manifold due to the age of the manifold and the lack of replacement parts.

I could get access to the pex from the radiator and either use a portable pump or use a hose connected to a faucet to test for flow? Bad idea?

skiereric

thank you for all your advise on this.  

I have isolated the supply and return pex from the radiator and have confirmed the supply pex is clogged or kinked.

I have been able to connect the pex to a hose fed from a sink.  The return flowed and spit out a large amount of sludge and later flowed clear.

The supply side is clogged. I have been trying to flush out from both the manifold side and the rad side. I’ve probably alternated at least 20 times and no luck. 

i am trying to snake a wire to manually clear the blockage but a 1/2" × 1/2" PEX Comp. Coupling about 6’ from the end of the pex (one is accessible at the manifold the one at the rad is not) has stopped the snake. 

Any advise? More PSI? Perhaps compressed air? Or a DIY pump?  Or should I just keep alternatives what side I flow water into?

mattmia2

Can you see the entire run of pex? My bet is that it is kinked somewhere.

skiereric

No, unfortunately not. The problem pex runs to my third floor and is under the floor, walls etc. 

It won’t be possible to get access to the complete run.

kcopp

Compressed air is your next best bet.