Toilet Water Flush valve.

That was the problem, a broken water valve. This was in the front head and very difficult place to work in. After I went as far as I cold without standing on my head(no pun here) I took the RV to a nearby repair facility. They had it ready for me the next day. I think it was worth the $120 they charged me. I have been doing business with these people for several yearsand have never regreted it.

I had to replace mine a couple of years ago of this very reason. On mine there was a front wrap around trim piece that was velcroed in place making it easy to remove. The valve is then bolted to the toilet and easy to remove. I got my new one at a local trailer sales lot, not the dealer I bought my 5er from.

The toilet is a Dometic/ Sealand

Sounds like water valve is broken.

You can go to toilet mfg. website and get manual with exploded view of parts.

Usually due to confined space/access it's easier to pull toilet off floor flange, take outside and repair/replace parts.

Which toilet do you have?
Sealand, thetford etc. and model