Greenstar 27 CDI circulation problem

[Mike2007]

Greenstar 27 CDI
9 radiators
8mm microbore
floors, ground, first and second all heated with rads

ONE of the these radiators will NOT heat. Its probably the futherest away from the boiler (sited on 1st floor)
Radiator has been removed, lockshield valves (2 of, no trv) have been tested and high pressure on both flow and return.
When radiator is filled, it fills quickly and with hot water. But from then on it does not circulate back to the boiler?
Tried locking off ALL RADS except the trouble one, but still it did not heat up?

I can't understand what is the problem?

Let me know what you think?

 

[Mike2007]

Why do my questions seem so difficult to answer? Please ask for any more details?

 

[Andygasman2010]

You have a blockage somewhere but I guess you already knew that.

Is it plastic pipe or copper?

Remember that there is a difference between pressure in your system and circulation.

A blockage can cause poor circulation but it doesn't affect the pressure in the system. So when you open a rad valve into a bucket it may appear good but it can be a bit of a red herring.

Sounds like you have a severe blockage that'll need locating and cutting out. Floors up time.

 

[Mike2007]

You have a blockage somewhere but I guess you already knew that.

Is it plastic pipe or copper?

Remember that there is a difference between pressure in your system and circulation.

A blockage can cause poor circulation but it doesn't affect the pressure in the system. So when you open a rad valve into a bucket it may appear good but it can be a bit of a red herring.

Sounds like you have a severe blockage that'll need locating and cutting out. Floors up time.

Thanks for that Andy. I did not know I could have good flow from the rad valve but still have a blockage in the circuit ?
Although I do understand 2 bar of pressure might still be 0 litres per minute!

 

[Andygasman2010]

Yea you're right. Pressure and flow are two different things. If you open a rad valve into a bucket you will have 2bar into atmospheric pressure, in your heating system you have 2bar either side of the blockage.

 

[Mike2007]

Must be a permanent blockage/ damage. I power flushed it today and the pump had a terrible time getting water through!
I reckon someone has hit microbore with a hammer whilst doing other services (upps..don't say anything moment)

 

[Andygasman2010]

If there is NO circulation at all then a a Powerflush machine won't touch it anyway. It doesn't pump at any higher pressure than the boiler will, just a higher flow rate.

It needs locating and cutting out.