Radiator with negative pressure on both ends

[pf79]

Hi,

I was wondering whether anyone had come across previously a radiator that appears to be under negative pressure from both Flow and Return ends.

Back story:
Moved into a property with a Gravity Feed HW and pumped CH system. The pump is located on the return side of the CH. Downstairs radiators are supplied from pipework in the concrete flooring.
Currently having a few issues getting the upstairs radiators to warm fully, especially my daughters room which is furthest from the boiler.
Did the usual thing of bleeding the radiators but to no avail. Actually first time round I bled them with the pump running, which caused air to be sucked into the radiator, which indicated that system was under negative pressure. Did them again without pump which filled the radiators but still not much heat. Noticed as well that some of the radiators had cold spots on them as well, so chucked in some cleaner, left it to run and set about this weekend draining the system and cleaning each radiator out with the garden hose.
Put it all back together, refilled from the drain point using garden hose in an attempt to push any air upwards that may be trapped and bled fully. Still no heat in my daughters room, even with all the other radiators turned off.
Took her radiator off again and switched pump off. Opened valves on both sides into a bucket to check the flow rate. Both seemed fine and water was coming out clean.
Turned pump back on again to see what would happen.
Here is the oddity
Opened what I expected to be the return and it sucked water out of the bucket.
Opened the flow and this too sucked water out of the bucket.

Now I would have thought that only one side would be able to suck water and the other would push water out due to circulation.

Is this normal???

Any advice welcome

Thanks

pf79

 

[snowhead]

Sounds like a 1 pipe system with Daughters radiator on the negative side of the pump.

 

[pf79]

Thanks for the reply snowhead.
It didn't even cross my mind that it could be a single pipe system.

I'll have to rip some of the floor up to confirm.

We are going to need a new boiler soon, so if it is a single pipe system I'll get a quote for replacing the lot with a 2 pipe system.

Thanks again.

pf79

 

[REDSAW]

overpumping

 

[Darren Jackson]

Try turning pump down

 

[pf79]

Hi,

Thanks to everyone that replied.
Had someone in to take a look today and discovered 2 corroded Non-Return Values on the Flow pipe to upstairs.
These have been stripped out and replaced with a single length of 22mm, which seems to have fixed it.
All radiators are now red hot. The negative pressure must have been caused by the restricted flow-rate on the Flow pipe.

Thanks again.

pf79