Could it be the snow?

Er… is there any sunlight? Even with a covering of frozen snow mine will pick up energy from the sun and the manifold temperature goes up.

At this time of year with the angle of the sun and the outside temperature mine are getting up to about 16 C. in sunny weather but with snow covering the tubes and no sun you’ve no chance.

No sunlight… I want magic….

actually getting it as well -2 outside no sum and 2inches of snow on the tubes…and they are still showing 17C
Sunny days I have been getting 55C

Bluddy ‘ell! How many tubes in your array and what orientation?

I’ve got 20 tubes facing SW and in May/June I get 58 and twice I’ve seen 60.

60 tubes (larger than standard tubes).