buckyuk

Hi Guys, Been learning a lot about how to care for our new tub from the forum, so thanks. But have a bit of a specific questions that i cant find any threads on so far, so here goes... We have a hydropool 670 self cleaning tub. I'm trying to figure out if there is a problem with the heater, or i just need to manage my expectations. We have tub set to 39.5oC. with about 4 of us using it, after say 40 mins. its down to 37oC, which doesnt feel very hot at all to be honest. Ambient temperature at the time here in Scotland is about 5oC. At first we thought it was a problem specific only to the pumps being on, but turns out the same happens even if we dont turn pumps on at all. Infact the other day i opened the lid, it dropped to 38 and didnt seem to recover even after an hour of sitting. Is this normal? When feeling the inlets in the tub when its trying to heat, none of the 3 feel particularly warm/warmer than the surrounding water. So yeah, just trying to see if anyone has similar experience or maybe this is just normal for hot tubs, but i feel like we went with a top of the range tub, and it should at least be able to hold a temp. Customer service has been particularly slow going back and forward and i'm starting to get a bit frustrated. Thanks in advance