Pool water much hotter than thermostat setting.

[Seamus71]

Complete newbie so forgive me if missing something obvious. Would appreciate any helpful advice.

New property has indoor heated pool. Twin gas boilers provide central heating for house radiators,
underfloor heating for house and pool heating via a bowman heat exchanger. Not really sure of how to control outflow temp from boiler. (Looks much more complicated than simple combi boiler in last house. I have set bowman digital thermostat to 28 C but thermostat showing current temp 35.8 C at top of heat exchanger, and still feel hot water being pumped into pool. I have tried setting timeswitch so that pump is only for 12 hours a day but by Early evening pool is like a warm bath again. Switching off the time switch turns pump and heater off which lets everything cool down but I assumed that if pool water temp was above thermostat setting then I should be able to to leave timeswitch on so pump would continue filtering without providing heat.
My gut feeling is either my thermostat is faulty or the valve that should shut off hot water from the boiler to the heat exchanger is faulty so heat exchange is always on.
Pool guy coming twice a week and checking water quality pH and chlorine, he recommended leaving pump on 24/7 but that is causing water temp to continue rising.
Not sure how I can have pump running without heating.

[Denniswiseman]

Somethings not right
I would look to the inlet from the boiler flow, there should be a motorised valve to shut off the flow from the boiler when it reaches temperature which should be linked to a thermostat on the Bowman (pool side water)
Either could be faulty or jammed MV (worth seeing if it can be freed or tested)

[Teapot]

Seconded!