Poor circulation on central heating (light commercial)

[tek2k]

I hope someone here can shed some light on my problem.

There appears to be some kind of circulation problem on the central heating side of the system but I am unsure of the cause.

We have a low loss header fed by two keston C55 boilers. When the bypass valve is closed there is a pressure increase as the pump starts to work harder and most radiators heat up fine but some do not.

When the bypass valve is opened water seems to circulate very easily around the central heating system and the bad radiators start to warm up however it seems that flow water stops going to the radiator circuit and flow and return just cool down. It would appear the bypass route is the easiest path for the water so it just goes that direction rather than back into the header.

As soon as the bypass is closed flow through the central heating gets hot but again there is a circulation issue.

Could there be a blockage of some kind on the return side or parts of the system blocked with iron oxide deposits?

Could it be the return from the megaflow circuit is causing resistance by trying to flow backwards through the return from the radiators?

The flow and return pipes into the header are 35mm. I would have thought this is large enough but I may be wrong.

Untitled

• tek2k
• 5 Jan 2009
• 1

 

[Tipper]

Are there non-return valves to stop reverse flow?

Are both pumps run at the same time?

Are both pumps actually working?

 

[tek2k]

Both sets of pumps are definitely working. On the radiator circuit return before the Tee connection there is something called a Tacometer which has a directional arrow but im not sure what it actually does.

I actually closed off the flow and return to the megaflow circuit but it had no effect.

The radiator circuit still seemed to be encountering resistance until I opened the bypass a little.

 

[simond]

I can't understand your post.

You mention 'bad' radiators but say they don't work when the bypass is closed.

When you open the bypass you say that the rads get warm but then the flow and returns cool down.

I can't see how the rads can warm up if there is no flow.

 

[tek2k]

The problem has been fixed. Found a special filter on the return pipe (not a y strainer but actually an inline filter) that was roughly 60% blocked with sediment. This was reducing the return pipe diameter by probably about half hence leading to poor circulation. We cleared it and circulation is much better. Next step will be to flush as much as possible of the system and readd inhibitor.

Thanks for the help.