Where to site fill and drain valves

[Trevor Jones]

I can't see any other valves apart from the one one the roof (which I don't have access to) and the one between the fill points. I know the one between the fill points opens because I can pump fluid from one port to the other if I open it.
I didn't need to drain the system in order to install the valves because that bit of pipe work didn't have fluid in it. I did start to drain down when I thought the pump might be jammed and got some clear orange fluid out which looks pretty much like the Fernox S1 I am trying to top up with.

[Trevor Jones]

Apologies Lucman there was a stopcock on the return pipework. I had mistaken it for the main cold riser. A bit of persuasion with some pliers and that was it. Have now managed to pump in all the fluid I have. I still can't get it to come out of the drain valve but the pressure on the gauge is up to 4 bar and the fluid seems to circulate so I will call it a day now. I have a man on standby to come and review it when lockdown is eased. Thanks for all the help.

[LucMan]

Great!
You probably have a small leak, most likely the bleed valve on the roof. Best to replace it when you can.

[peakbagger]

I still have a air bleed valve on my roof but expect long ago it gummed up closed. With a proper pump station,for recharging there really is no need for one. I use a 5 gallon bucket to fill and purge my system but wish I had bigger one on the rare occasions I have had to work on my system.

There are not a lot of evacuated tube systems in long term operation compared to flat plates. Don't waste your time fixing the system until you find someone with thermal scanner to scan the tubes, odds are many will be dead.

I have friend with flat plate system than is close to 40 years old. The only maintenance is making sure the check valve is working. He checks his pH and I think he still is on his original ethylene glycol charge. My flat plates are 20 years old and still working fine. It has DC pump an PV panel to run the pump and its the original pump and brushes. The PV panel on the other hand is looking pretty toasty but still works.

[Trevor Jones]

I made another mistake. When the sun came out I discovered the fluid wasn't circulating, but some did come out of the pressure relief valve. This joined the circuit just before the pump, so figured that one of the valves either side of the pump must be stuck. Waited for a dull day and drained the system down again. Took the pump, with the two valves still attached off. Sure enough the lower valve was blocking the flow even though you could wind the shaft in and out. Had to stick it in the vice in order to get the valve off the pump. Fitted a new one and hey presto when I filled it this time fluid came out of the drain valve. Need to wait for a sunny day now to see if it's finally fixed.

Yes peakbagger, we used to have a flat plate on the roof but when we had a new hot tank fitted a few years back was persuaded to change to evacuated tube. I have regretted it ever since. Just trying to make the most of it now. At least this lockdown has made me attempt the job myself and thanks to the help on this forum saved me a bit of cash.