Rover 25 heater not warming up and water tank using a lot of water no leaks visable

you have a coolant leak somewhere,is the water and oil mixing,check your oil filler cap and dipstick for signs of brown sludge,get a block test done to check if headgasket is knackered as this is a common fault on this engine,also get a pressure test done on cooling system if not done already

will this cost alot or not

if the head gasket is gone you are looking at a few hundred quid for parts and labour,and extra if head needs skimming due to warping,is there any smoke from exhaust or smells?

thanks i will get it checked out and let u know the outcome

You dont say what engine in car ,so hard to give you a cost for head gasket repair if that is what is wrong . Head gasket very common on that car and expensive to repair correctly .Here are some prices from Rover forum for 1.4 engine

"
strip, pressure test, skim, all new gaskets, timing belt, water pump, oil, filter, rebuild, system flush, new coolant, around £450, get it to s wales and i'll do it for you... anything else like rad, rear metal pipe etc extra, but this is very rare... "

" For water pump and timing belt to be changed as well as the headgasket id budget anywhere between £400-500, and thats at an independent garage, but your right the water pump and timing belt should be changed at the same time. "


£300 - £400 from an independent, £500 - £700 from a dealer.

If you handy with a spanner and have a weekend free you could try doing it yourself, there are a few threads about, trying looking in the How To section and think of the knowledge you'll gain.
And

"i paid £422 to get mine done

SJ "