Central heating issue

[keredwh]

This is an odd one.

For a few days noticed downstairs radiators not getting hot from late morning onwards although upstairs ones seem fine.

Pump is less than 12 months old, divertor valve about 18 months old.

Can hear and feel the pump working and have checked the spindle which is spinning fine.

Last night, downstairs radiators freezing, upstairs radiators fine.

Got up this morning, all upstairs and down radiators nicely warm!

It's now early afternoon and the downstairs radiators are freezing and won't warm up again!

All radiators have been bled.

Timer is brand new and set up correctly. Thermostat appears fine and clicks on and off but downstairs never gets up to temperature because radiators are freezing!

Any ideas?

Thanks

 

[Armo74]

Have you tried balancing the system?
Is there a pattern like upstairs getting hot when only hot water is called for?

 

[Jackrae]

Do you have zone valves and if so are they opening

 

[keredwh]

Have you tried balancing the system?
Is there a pattern like upstairs getting hot when only hot water is called for?

I haven't tried balancing but only because nothing has been altered since the last plumber fitted the new pump.

No there doesn't appear to be a pattern except that in the morning, everything seems fine but as soon as the radiators cool down, they never heat up again!