2 New Radiators Not Heating

s2225

We installed two new radiators on the second floor with 3/4 o2 pex. The feed goes up from the basement
to the first radiator from one of the takeoffs. Then goes out of that radiator into the next one. From there it then return all the way to the basement return line. I let the system run at 15 psi today for 2 hours, bled the radiators and only feel heat on the first foot of the pex takeoff and pex return in the basement. I'm confused because further down the line there is another takeoff that is heating as expected. Any ideas what to do next? All other radiators in the home are heating properly. I did notice the expansion tank is very full feeling.

Thanks.

Ironman

What type of radiators? If they're CI, then they need to be piped individually. And that's what your pic indicates.

Also: water takes the path of least resistance. If all the other rad's have larger piping going to them, then there's less resistance in them than in the pex you ran.

If the above scenario is accurate, you may be able to get flow by adding a circulator in the new loop.

s2225

The existing ones are cast iron, but the two Daisy chained new ones are the modern British steel style bathroom Radiators from Hudson Reed. I was wondering about adding an additional circulator. Currently, I have the Taco 007-F5 Cast Iron Circulator, 1/25 HP at the boiler.

How would I add a second circulator and what size/speed? The full expansion tank wouldn't cause this issue of?

Thanks.

Jamie Hall

The full expansion tank will show up as an excessive pressure rise in your system as it heats up. Excessive being open to interpretation -- but anything more than just a few psi is excessive.

The steel radiators -- particularly if daisy chained -- have much more head loss than the CI ones, so you will need a circulator for that circuit.

s2225

What pump should I add for this and how would I install it in that location? Run electrical from the first pump? Install on the pex return side I assume?

Thanks.

Gilmorrie

Until the possibility is eliminated, I would suspect air blocking flow.

s2225

I did bleed both problem radiators till some water came out. How else would I determine/address airblock situation?

Thanks.

Zman

It would help if you drew out the whole system. The original likely has very little resistance. Pex has a fairly small ID as compared to steel or copper thus more resistance.
It is likely that you need to either add a circ or some balancing valves to get this working.

s2225

I was able to get heat to the radiators after significantly closing down valves at downstream and upstream cast iron radiators. Boiler is reading almost 20 psi when hot. Is this ok for a 2 story house with basement?

Thanks.

Ironman

20 psi hot is fine.

I'd add a small circulator (Taco 007 or Grundfos ups15-58) at the supply branch to the new rad's.

s2225

If there is flow to the new radiators on the branch now that I have almost closed many of the other radiators, would I really need the additional pump? Assuming the old almost closed radiators are still getting hot enough.

Thanks.