4 year old Boiler losing pressure, how much will it cost?

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Dh is constantly having kittens over our boiler. He worries we will need a new one.

Twice this week the boiler has lost pressure in the morning and we have to manually fill it up.

What could cause this?

We have a British Gas check for it to be insured in 2 weeks and he’s worried that if soemthing is wrong they won’t fix it. 😑

Advice please!

Our combi boiler regularly lost pressure around twice a week at 6yo.
Our boiler man replaced a part that had failed and topped up some fluid to stop scale inside and it came to £260.

On ours there was a leak coming from the boiler, a slow drip. It is in the garage so we didn't notice it.

I hope it gets sorted soon.

He did say it could have come from a leaky radiator, but it would be noticeable to be losing pressure that fast.

is there a warranty? ours is Bosch and we've had for nearly 5 years and covered under warranty still.

I had a faulty expansion tank that made mine lose pressure.
About £200 to repair.

Ours has done this a couple of times. Never more than £100, just a simple valve or something.

Our 7-yr old Bosch combi needs topping up a small amount about 4/5 times a year. Have had it serviced and checked twice by 2 different plumbers and they can't see why. Checked rads and outside pipe. They said carry on as we are!