Abbey Blonde stall

[Lab Cat]

I've brewed this before with no issues. Brewing again, to the recipe as before. This time it's stuck on 1.020 after5 days, hasn't moved since Saturday. Yesterday I put the temp up to 24 but it's not moved. Last time I did this it got to the Ianh predicted 1.010, and it should with 2 Belgian yeasts in it, even if they are lower attenuation.

Any ideas what the issue is? I've added a little Nottingham slurry, I'm not bottling it at 1020 and this is the only thing I can think of.