T&P valve, horizontal okay?

CBRob

Have a home I took on for management that has solar thermal.
The effectiveness of solar thermal on a vacation home is a whole other subject...
But this valve has been leaking for who knows how long.
Before I replace it and refill the loop, is it ok in the horizontal position?
It says: "install at the top of the boiler in the vertical position."
On the tag.

Mad Dog_2

It will usually work, but they don't want the the elbow they connect to becoming a Dirty mud and grit repository.  If you're dropping the solar,  do it right...Upright...Mad Dog 🐕 

hot_rod

consider a solar specific relief valve, you want a valve rated at 300F
Id also go with a higher pressure, 60 psi or more
Stagnation conditions will drive pressure and temperature way up
Caleffi has 320F valves up to 150 psi

Install an Ell and turn it vertical 

What expansion tank? That too should be a solar model.

Put a relief tube into an empty 5 gallon bucket so you don’t lose glycol if it triggers

Drainback or steamback is a better option for vacation or lightly used systems

check that glycol with a ph meter often. Stagnation conditions cooks glycol quickly, use solar temperature glycol

some good deals on e-bay

EBEBRATT-Ed

I always thought a T & P goes on and protects a tank, and a normal relief valve goes on the piping

hot_rod

Its a 30 psi valve, so I assume it is on the solar loop?

CBRob

This pressure relief valve is on the in-floor side of the heat exchanger. 
I'll probably get it up and running for the winter season and suggest that the owner look into removing the solar thermal part of the system for long term.
It's a second home now, no way to utilize the heat all summer long. 
It seems like a big liability to me.
I did just watch Bob's video on solar thermal, this house doesn't make good use of the system.
I'll ask around about a drain back option, out of my scope of knowledge.

CBRob