Circulating Pump Valves

[PaulForward]

Hi - I'm hoping that I'm posting this is the correct section.

Some impartial advice would be appreciated....

I have replaced both the gate-type pump valves on my DHW/CH system. Since replacing the valves, my downstairs radiators are only getting luke-warm, and the furthest radiator isn't getting warm at all. All radiators are bled of air.

Before fitting the valves, I did note that although the valves are 22mm, inside the compression fitting they narrow down to an internal diametre of around 15mm. I also noted that this wasn't the case with the old valves that I took out, which looked approximately 22mm all the way through them when the valves were fully opened.

I have been assured by the reputable dealer that I bought the valves from that this narrowing in the bore size of the valves won't make any difference, but this still leaves me with the problem of almost cold rad's downstairs.

Obviously I had to drain the system to replace the valves, and consequently I had to bleed the air out of the system. I did this several times, and left the heating and hot water running for the best part of a day. After that time, the pipework had become quiet of air, and the air-bleed valve had stopped ommiting air.

Any ideas, please?

 

[WHPES]

Sounds like you may have some air locked in the pipework somewhere. Turn the pump to max, turn off the DHW circuit, shut down all but one radiator, fully open the rad valve and lockshield. Go through each radiator one by one. This is usually enough to blow air out.

 

[stevetheplumber]

if bleeeding dont work id change the valves again as thats the only thing thats been altered at least then you would eliminate them as the problem

 

[willing2learn]

May seem obvious...but are the new pump valves open? Also...maybe it has disturbed some sludge in the system? Or may need re-balancing?

 

[bobpape]

If you have restricted the flow or return by any amount you would need to compensate
by increasing the speed of flow which may make the system noisier,

Ball park figure at a quite pump speed is 13000 BTUs (3.8 KW) through a 15mm pipe
and 60000 BTUs (17.5 KW) through a 22mm pipe

 

[Bernie2]

Hmm!

Obviously if you have restricted the input and output something is going to happen. Pumps such as Grundfos 15-50's have only got a 15mm nominal bore and its output 50 kPa or just over 5 metres head.

If your pump had been on its limit at number 3 with the old valves, the slight flow restriction down to 15mm may cause problems, requiring a bigger pump.

If not try for air problems or possible cavitation.

 

[WOLDEN]

have you put the pump back the right way , arrow for flow direction