Primatic system (again) one rad not working?!?

Hello to all of u again!

Hmmm, ive still got problems with this primatic, one pipe system...any of u SuperPlumbers got any ideas?

I drained the system and refilled it. Everything is going well except for the rad in the bathroom. When the heating is on, the pipes to the bathroom rad are cold and sometimes a little bit warm and its impossible to bleed the rad (seems like there is no water going to the rad to fill it) BUT when the heating is turned off, the pipe to the rad gets warm and loads of air can be bled from the rad until its full of water and it warms up a little bit. Then when the heating is turned on again the pipe to the rad gets cold and again it seems that the rad cannot be bled?!? I had better mention again that the heating system is a one-pipe type.

Any of u guys got any ideas or explanations...im stumped!

Thanks...Jimbobplumb

Hope everyones not too busy...if it snows, take a day off and get the sleigh out of the shed!

Bear in mind that bathroom rads were sometimes connected to the gravity primary pipes to the cylinder rather than the pumped heating pipe so that they would be hot year round.

However that doesn't seem to fit with the venting of the bathroom rad depending on whether the pump is on or not. That suggests that the bathroom rad connects to the suction side of the pump and so attempts to vent air when pump running result in air being drawn in.

Venting should only be done when the system is static (no pump) to avoid problems like this. There could be sludge restrictions in pipework which exaggerate the negative pressure on the suction side of pump.

Thanx for your reply Chrishutt!

I was also thinking that it might be something to do with sludge buildup, i really dont like primatic systems!!

I think u might be on the right lines with the rad being on the suction side of the pump...when i bleed the rad until it is full (with the heating switched off) and then turn the heating on, there are no air or bubble type of sounds actually in the rad, but then if i try to bleed it again with the heating off there seems to be loads of air in the rad again? Seems as though the water is being sucked out of the rad!?! Its kind of weird i know.

Any ideas matey of how to get this rad hot again?? Im afraid that if i keep bleeding the rad then i could possibly disturb the air bubble inside the cylinder. Also, the pump is turned to its lowest speed, do u think i could turn up the pump speed a little and not disturb the cylinders air bubble?

I appreciate any ideas coz my hair is turning grey over this!

Chrishutt?? Where have u gone

Does anybody else think that increasing the speed of the pump will get the rad hot? I just dunno what to do next...i dont want to admit defeat and get her to call another plumber (unless its one of u guys!!)

Seems as though the water is being sucked out of the rad!?!

Click to expand...

It can happen if the suction of the pump exerts more negative pressure than the head of water can exert positive pressure. You get sub-atmospheric pressure and then air can leak in quite easily. Setting the pump to a higher speed will make such problems worse.

Beyond that I don't think I can suggest much without actually being there. It's very difficult to get a picture of whats happening otherwise. Could be air locks, sludge, combination of those things. Sorry.