Hot radiators upstairs but cold downstairs, this will test y

[bennyboy76]

We have a Potterton Performa combination boiler that has had the following replaced in the last week; pump, diverter valve, PRV, hot water heat exchange, central heating heat exchange. We have also had the system flushed and I have ensured again there is no air in the rads.
Upstairs is toasty with the rads open on barely half a turn. Tonnes of hot water so no issue there. If I shut them all the rads downstairs start to warm.
Parting words of today's engineer was 'blocked pipe' somewhere. Any other suggestions or how we could detect where a block might be?

 

[Ihavenojob]

Blocked filter in the return isolation valve.

 

[bennyboy76]

Just checked the paperwork and BG state they changed the return filter, I not that the temp sensor was also changed.

 

[xr4x4]

Start to warm, or get hot?

 

[bennyboy76]

Start to warm but as there are six downstairs they take a while, there are three upstairs.

 

[xr4x4]

You need to leave it longer.

 

[bennyboy76]

Thanks Paul, I should state that all rads are open and boiler has been on since 16:00. It heats the water then turns off, upstairs are hot but downstairs cold. Downstairs will only start to warm if I shut the upstairs ones completely.

 

[xr4x4]

To clarify, you need to turn off all your upstairs rads, so they don't get hot.

Also turn off the hot water.

Fire up the heating and leave it on, for as long as you need.

Do the downstairs rads get hot? Or just stay warm.

 

[bennyboy76]

So, upstairs rads closed and all downstairs rads get hot except for the furthest one. Reopened upstairs and now the downstairs ones are cooling down. How can they be a blocked pipe?

 

[xr4x4]

It's not....

It's balancing.

Some rads may only need opening qtr turn.

 

[St0rmer66]

Existing gravity check valve from the old boiler which has now started sticking shut. Common problem. Needs to be removed.