It sounds a lack of water pressure. Some of these things to do with water pressure can be weird.
I connected my merlin up originally in the bathroom as the info said it would run off mains pressure but no water came out the merlin at all.
I reconnected it to the pipe as it comes into our flat and it worked fine at 25 ltrs about every 40 minutes.
I can't remember what the pressure was but according to the pressure gauge, the pressure was the same in both places. A plumber did explain it to me but I didn't get what he was on about but to the plumber, it made sense.
I've now plumbed it in the kitchen and use a booster pump and I get 25 litres every 30 odd minutes at 6.1 bar.