Pump Problems?

Another amateur I\\\'m afraid!!

I have an oil fired boiler (Boulter - Camray Compact) with expansion vessel (BOSF - 18 litres) and pump (Grundfos Type UPS 15-50).

We have just had a largish extension built (for the size of the house) which has 3 brand new radiators. If I turn all the radiators in the house off - and leave the radiators in the extension on - they heat up well. They are lower than the boiler but the furthest away from the boiler.

When I turn on 2 or 3 of the radiators in the house they gradually take heat from the radiators in the extension (until the radiators in the extension are lukewarm).

If I turn all the radiators on - the radiators upstairs are the only ones which work - leaving all the other radiators cold (all downstairs) ...

The pump \\\"seems\\\" to be working (it moves, whirs and gets hot) and the pressure in the system is at 1 bar (just over) ... I have also bled all the radiators until water drips out.. I know the answer is to get a plumber (and I will in due course) ... is there something I ought to be trying to save me the hassle?

If you're saying that all the rads work some of the time, but not all the rads will work simultaneously, then you need to balance the system (assuming the pump is OK). If you do a search on balancing you will find some detailed discussion of it, but basically it means increasing resistance to flow through the rads that heat up most easily by progressively closing the "lock-shield" valve on the rad.

A possible complication to consider is that the draining and refilling of the system may have caused some air locking and may have shifted sludge to block pipes (usually at low parts of system).

Thanks Chris - I'll try this ... I don't think we'll hit sludge complications as I have needed to drain the system in the past (within the last 3 months) and the water that came out was pretty clear ...

But yes - I am indeed saying that all the radiators work some of the time but not all simultaneously (so I'll try balancing them)

I have read that hot radiators upstairs and cold downstairs can mean a pump problem ... can these same symptoms also relate to a balancing problem?