We recently had to change our boiler because the original one became obsolete and sprung a serious leak but since it lasted 19 years I'm not complaining.
The new boiler seems to be okay with the heating because while it was being set to work (we had TRV's fitted to our rads at the same time) the house was like a sauna. However, the hot water is not very hot and while this was previously a problem with the old boiler I thought it might go away when we changed boilers!
At the moment the cylinder stat is set at 70 degrees but the water from the taps is lukewarm. According to the boiler manual, the control on the boiler only adjusts the central heating temperature and for hotter water I should change the cylinder stat so I don't see any point changing the boiler control.
The cylinder stat has been changed and relocated to a "better position" on the cylinder earlier this year but the problem persists.
Incidentally, for a few weeks back while we were planning for the new boiler we were using the immersion heater and the water from the same cylinder was very hot so I'm now confused!
The water is heated by a copper coil inside the cylinder. The coil is heated by the boiler. So you could have a very poor flow through the coil. There could be many reasons for this, and I would have thought that your installer would have spotted a problem when the boiler was installed. There is often a valve fitted near the cylinder, used to balance the flow. With a bit of luck a slight adjustment may solve the problem. Could you post a photo of the system just around the cylinder. We would then get a better idea of what's going on.
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