Pulsacoil 180 - newly installed and faulty

We had a Pulsacoil 180 installed approximately 5 weeks ago to replace the Pulsacoil 2000.

One morning we woke up to no hot water. Got the plumber back which took 2 weeks as he was abroad. He came, don’t know what he did as my partner was home but it rectified the issue.

It went off again 2 days later but then started working again 3 days later.

The tank feels warm, when you run the hot tap you can hear it click as it registers the flow but the hot water doesn’t come through so I think it is linked to the pump.

My partner contacted the plumber again who said it’s nothing to do with him and we need to contact the manufacturer.

Is this standard practice?

Thanks