I have a BAXI combi boiler, which is about four years old. The central heating works well, but there is no hot water. Why is that?

My advice to you is to call a qualified BAXI contractor for a one site inspection and repair.

Now to answer the question.

A bad pressure pump
A bad diaphram
A bad micro switch switch in the brass hat area.

These units are not user friendly and should have professional service for safety and longevity.

That sounds like bogus info to try to discourage DIY. I had a similar problem. Try replacing the NTC sensor or the Hall Effect (or Flow) Sensor.

I really take offense to the fact that you are telling a person that has no idea what you are talking about to just start replacing expensive parts. You need to read there questions very carefully to see what there level of expertize is and then answer appropriately.

Thanks for trying to help but look at the dates first. There are a lot of questions from the past month that need to be properly answered.

Last but not least this post is from 8/4/2008 which is getting close to 4 years old so I hope he has it fixed by now.

Those parts cost $10 and $17, respectively -and they are very easy to install. There is nothing in the original post that suggests the person has no idea of what I am talking about. I am offended by so called experts misinforming people, presumably just to generate more business. I had a leak in my old washer, and one so-called expert had me trying to access the pump by taking the top of the washer off (the pump is on bottom). When I mentioned the parts you described to my HVAC specialist, he laughed. I know the post is old, but it is still active and actively misinforming people. BAXI does provide real customer support and there are local HVAC that are interested in helping people who want to help themselves. I post because I want the DIY community to to know that they have to read these posts carefully, lest they be discouraged misinformation.

Good luck with your endeavors.