Myson T6 Radiator Won't Heat Up after Bleeding

gadolphus57

I installed a Myson T6 radiator using the center supply/return valves. It is installed on a loop. The loop has one other radiator on it (an old cast iron).

I bled both radiators until water came out the air valves. The system is filled and pressured to the max (15 PSI). All the other radiators in the house heat up without issue.

However, the two radiators on this loop won't heat up at all under normal operation. They DO heat up if I open one of the air valves and let it bleed water into a bucket for several minutes; then, hot water will eventually start to come out of the air valve and the radiator will heat up. But if I close the valves and just let the boiler run for a while, there is no heat on this loop. The pipes feeding the supply and return don't even get warm, so it seems that no hot water is entering the loop at all. (Yes, the valves that control the supply and return lines to this loop are fully open.)

This loop used to have just one radiator on it (the old cast iron) and that did heat up without issue. So I know the supply and return pipes work.

I'm at a loss as to what could be wrong. Any ideas?

I am a little confused by the Myson's built-in thermostat valve and am wondering if that is where I am screwing up. It's a green piece that came preinstalled on the righthand top side of the radiator (when you are facing it) that has the letter N on it, along with several numbers. I gather that this should control how much water enters or leaves the radiator, although I am confused by how one sets it (the comic book installation instructions that came with the radiator don't make it very clear). I have tried moving it to various positions and it doesn't make a difference, however.

Ironman

Need some pics showing how you piped it. If you put the rad's in series, it won't work. And it probably won't work very well if they both are on the same loop: water takes the path of least resistance and it will go through the larger piping on the cast iron rad before it goes through the Myson.

metrorental

in addition to the previous comment, pls make sure the supply pipe is on the left and the return on the right when facing the panel. also, to ensure maximum flow, the N on the therm valve should line up with the notch in the brass base

Paul48

To bleed emitters on a loop, you have to have flow in one direction. I'll attempt to explain...........draw a loop with 2 emitters at the top......immediately to the left of the emitters there is an auto-fill regulator attached. Immediately to the right of the emitters and in the piping is your air. See it? As you bleed each radiator the auto-fill will send plenty of water, but the air will just sit there. Valve off the loop and put boiler drains on it. You can then fill with a garden hose, and let another hose go on the lawn.

gadolphus57

Thanks much for the replies. I appreciate them. Here is a diagram showing how the two units are piped. Please let me know if I've done something obviously wrong:



As the picture tries to indicate, the radiator is connected using the center connections, with the supply on left the left. I do have the valve turned to "N."

water takes the path of least resistance and it will go through the larger piping on the cast iron rad before it goes through the Myson

True, but in that case the cast iron radiator should at least be heating up, right? It doesn't even start to get warm.

EDIT: By the way, the air valve on the Myson had a preinstalled black plastic piece on it on the inside of the radiator. I took the air valve out, broke the piece plastic piece off, then reinstalled the air valve, because that is what the comic book character in the instructions seemed to indicate I should do. Was that a mistake?

Ironman

Again, water will take the path of least resistance. Think it out further: you've piped the Myson with its 1/2" connections and flow setter in series with the cast iron rad; the other CI rad's have large, unrestricted pipes; what's the path(s) of least resistance? Obviously, through the other rad's. When you piped it in series like that, it's like the weakest link in a chain: the Myson is restricting flow to the other rad.

Even if you were to pipe the Myson separately (as it should be), you will get little or no flow through because it's more restrictive than the CI rad's and their larger piping. You could add another circulator to the branch feeding the Myson and it would probably perform satisfactory. But the CI rad needs to be on its own branch, not in series with the Myson.

gadolphus57

I understand what you're saying about the path of least resistance, but if water were not wanting to flow through this loop because of the Myson's smaller piping diameter, why does hot water flow so readily out of the air bleed valve on the Myson when I open it? The hot water goes through both radiators in that case without issue.

And if restricted water flow were the issue, couldn't I expect the radiators to at least get somewhat warm? Even if I run the boiler for several hours straight, it seems that absolutely no hot water reaches this loop.

I'm not questioning what you're saying, but just trying to help myself understand better what I did wrong.

Ironman

You're making the common mistake of confusing the causes of two different types of flow.

Water flows when you open the bleed valve because the system has at least 12 psi static pressure and there's 0 psi on the outlet of bleeder. The circulator is not involved with this in any way.

When the pump runs, it creates a pressure differential of about 5 psi WITHIN the system. This pressure differential causes flow through the paths of least resistance: namely, the CI rad's and their larger pipes.

With the bleeder open, the only path for flow is through it to the atmosphere. With the bleeder closed and the circulator running, it finds multiple paths through the larger pipes, but not through the smaller more restrictive pipes and Myson.

gadolphus57

That makes sense. Thanks.

So I guess my question now is whether there is anything I can do to fix the situation, short of repiping my entire heating system or replacing the Myson (which was not cheap, so I'd feel dumb if I end up not being able to use it).

As mentioned, perhaps installing a circulator to feed the Myson would get the job done. Do they sell tiny circulators designed for this purpose? If so, what would I google to find one? All I can find are the large circulators that you install near the boiler.

Anything else that would remedy this?

By the way, wouldn't this same issue basically occur if you have a system that mixes cast iron with fin/slant baseboard heat? The baseboards would have a much smaller diameter, so they wouldn't heat either, right? But it seems to me that it's not entirely uncommon to see houses that have cast iron in some rooms and baseboard in others, so I'm hoping there's a way to do that and that I'm not out of luck in my situation.

Ironman

It's a situation that happens all too often. In fact, I just came from a job this afternoon where that had been done and the results were the same.

Get a Grundfos UPS15-58 and run it on low speed. Pump into the rad, not out of it. In other words, put the circ on the supply branch. You may get it to pump through both rad's the way you now have it, but the Myson will have less output because it's being supplied by the cooler water coming out of the first rad.

gadolphus57

Thanks much. I'll look into the circulator.

One last question, mostly out of curiosity: On the first floor of my house, the radiator supply and return pipes are all 1.5 inches. On the second floor they are 1 inch. (I know because I have had to replace leaky valves.)

Why would they have piped it this way? Per the path-of-least-resistance principle, wouldn't having smaller-diameter pipes on the second story slow the flow to radiators on that floor?

In practice that is not the case. Apart from this new loop that is giving me problems, all other radiators in my house -- which are all cast iron, except the Myson -- heat up pretty quickly (for cast iron, at least) and evenly. The first-floor units get hot maybe a little sooner than those on the second story, but there's not really a big difference.

Ironman

Your system was originally gravity flow - no circulator. The hotter water was lighter and would rise to the top of the system first causing the upper floor to heat more than the lower. To compensate, the dead men ran smaller risers to the 2nd floor. Once a circulator was added, the effect became just the opposite because there's less resistance to flow through the downstairs rads. Try partially closing the valves on those to force more flow upstairs.

gadolphus57

Aha, that makes a lot of sense. Thanks. I've always wondered why they did it that way.

I guess that means I should have a decent chance of still getting water to circulate somewhat effectively via gravity in the event that the circulator broke or we had a power outage, right (and assuming I could get the boiler to fire up in the latter case without electric)? That would make me feel better; having my house freeze during a storm that knocks out power is one of my perennial fears.

Ironman

It depends on the of boiler you now have, how it's piped and whether there are and flow checks in the circulator(s) or piping.

If it has 24V controls, it's not gonna run during a power outage.

pageyjim

gadolphus57 said:

Thanks much for the replies. I appreciate them. Here is a diagram showing how the two units are piped. Please let me know if I've done something obviously wrong:



As the picture tries to indicate, the radiator is connected using the center connections, with the supply on left the left. I do have the valve turned to "N."

water takes the path of least resistance and it will go through the larger piping on the cast iron rad before it goes through the Myson

True, but in that case the cast iron radiator should at least be heating up, right? It doesn't even start to get warm.

EDIT: By the way, the air valve on the Myson had a preinstalled black plastic piece on it on the inside of the radiator. I took the air valve out, broke the piece plastic piece off, then reinstalled the air valve, because that is what the comic book character in the instructions seemed to indicate I should do. Was that a mistake?

I don't know if it is related to your problem but I believe you are only supposed to break off that piece in the bleeder if you use the side connections.