Vaillant EcoTec 28 not heating up radiators as quick after a routine service

[trebarwith33]

We had a service the other day and since then we've noticed it takes a long time for the radiators to heat up. e.g this morning the heating was on for 2 hours and it only really took the chill off the rooms, but wasn't warm. Usually 2 hrs would be more than enough to become uncomfortably warm. I noticed the boiler only reached around 45-50c after 2hrs of being on!

In addition to the boiler service, we also got the plumber to install the Drayton Wiser Hub.
Previously the only controls we had were the timeswitch which broke a while back, hence getting the Drayton system installed note: we haven't even installed the Wiser rad stats yet, so in terms of balancing/calibration etc everything is exactly as it was before - except the hub is installed.
The plumber showed me he had removed the connection from the timeswitch and the on/timer/off switch so that is completely disabled now. It was left in place as we don't have the blanking plate.

My understanding is that the Drayton Wiser system only calls for heat so doesn't have any control or modulation of the temperature of the boiler so don't think it's related to any of the Wiser settings or configuration as such. The Wiser system seems to work ok, the boiler fires up on schedule, but just doesn't seem to run at full power.

One thing I noticed is that the radiator icon is continuously flashing. I don't remember this happening previously, I thought it was always solid when the heating was on.
After googling it, I believe flashing means there's a call for heat, but boiler is not heating as water is already at temp. Solid means the boiler is heating.
But... in my case it flashes constantly e.g its flashing now with the temp at 44c, meaning it's not heating, just running the pump? The target flow temp is set to 65c.

The service was fine, he said there were no issues. Also hot water is working as normal.

Any ideas what has happened or suggestions of things to check?

Thanks

 

[CBW]

What did the service engineer say, or have you not contacted them? Have a look for a fully or partially closed valve, including magnetic filter (if you have one), as I’ve had similar before. Are you sure the heating target is 65?

 

[trebarwith33]

Not contacted them yet.
Double checked and yes, heating is set to 65c.
Couldn't see any obviously closed valves besides the filling loop. We do have a magnetic filter.

Interestingly, I turned the heating off, waited 5 mins for anti-cycling to end and turned it back on. This time it worked correctly, fired up loudly like it usually does, reached 65c and rads were hot. So I assume this means all valves are in correct positions etc? Pressure was 1.4 bar when I checked it while heating was on and a bit lower when off, but always within the marked range.

Similar behaviour reported here in this post and in the last comment, but no solution.
https://www.diynot.com/diy/threads/vaillant-ecotec-plus-837-issue-radiators-slow-to-heat-up.424057