I have the same boiler and recently fitted a Sunvic TLX stat also. I
like yourself found that the swing in temperature between on/off was too
great. I took it back and replaced it with a Drayton Digistat which is
much better the temperature now remains at a constant 22 degrees which I
have it set at after initial warm up and it does not overshoot during
initial the warm up also.

Marc

bobby wrote:

I have a Worcester 28i combi boiler with an attached Sunvic TLX thermostat
and things are working ok... but then not really.

The boiler is working fine. No problem.

The thermostat should turn heating on and off to keep room temperature
within a tight range. Mine doesn't. At the current setting the boiler
doesn't start heating until the temperature reached about 17 degrees and it
doesn't switch the boiler off until room temperature has reached about 27
degrees. The result is that I manually use the dial on the thermostat to
turn heating on and off. Less than ideal!

What should I do?

I hesitate to replace with another Sunvic TLX (or equivalent) as I fear the
same results. Somehow believe a digital thermostat would do a better job but
I don't know which are compatible with the Worcester 28i.

Thanks for any comments.