No Heat in Downstairs Radiators/8 mnth old Combi Boiler

Bendy_House

That looks like one of the isolating valves. There are two, one on the boiler FLOW and one on the RETURN. If you close these off, the water cannot circulate out of the boiler, and the boiler is completely isolated from the rest of your system - the rads, etc.
Ok, what made it half-off?! Two possible explanations that I can think of; the first is that someone in your house intentionally or accidentally turned it, cables, wires, toasters or whatevs. This is EXTREMELY unlikely, quite implausible. You will likely have found that the valve was quite firm to turn? And it's tucked well under the boiler? It didn't happen by accident. Deliberate, then? Well, only you know if there's someone in your household with itchy fingers. I have to say that this, too, is extremely unlikely.
That leaves that the valve was left half-closed from the installation. Why did it take this time to reveal itself? A possibility is that its narrowed orifice allowed a build-up of sludge there, and it narrowed even further. That's just a 'possibility', but it's more possible and plausible that it having been turned accidentally or deliberately by someone in your house.
The installer or another plumber has no been out since the installation?

bris

Where is the filter and the boiler, upstairs or downstairs? Filters are usually at the boiler, if its upstairs the there is nothing wrong with the filter. Boilers work with flow and returm the water flows in then out back round the boiler. if the filter was blocked then there would be no return, The boiler is smart it knows there is no return and it shuts off.

If its downstairs then same thing, the blockage would stop all water getting upstairs and would shut off.

I doubt very much it's the filter

Bendy_House

We now know what it was - a partially closed boiler isolating valve.
A blocked filter could also have given these symptoms, but we only wanted the op to check it just to see the condition of their system.
Yes, the filter is near the boiler (looks to be on the 'flow', surprisingly), but it could restrict flow wherever it was located, surely?

shiraz99

Is that pic showing the filling loop for the boiler. Could it not be that when you topped up the boiler pressure you left the tap flow or isolation side turned on?

Bendy_House

shiraz99 said:

Is that pic showing the filling loop for the boiler. Could it not be that when you topped up the boiler pressure you left the tap flow or isolation side turned on?

Ooh, good point. The two blue taps are the top-up, and the miscreant black tap is behind it. But I wonder if someone could have turned the wrong '!!!!!! when trying to top up?

Hmmmmm...