What are the most efficient settings for a worcester heatslave?

[Balmeadie]

Folks,
I have an old worcester heatslave 15/19 combi, these boilers have a small HW store but other than that operate in the same way as a conventional combi. It's a sealed system with an open flue, no room stats just TRVs bar one rad.
In the vain hope that I could reduce the oil consumption of this old girl I turned down the HW and CH boiler settings to 2 (settings range from 1-6), the boiler now seems to short cycle, it seems to be constantly firing with very short pauses in between, the very opposite of what I wanted.
QUESTIONS
1. Have I caused this by messing with the controls.what should they ideally be?
2. What are the most efficient settings.( currently HW is on Constant 24hrs and CH is on 6-9am then 5-10pm ) ?
3. The boiler kicks in and out as I move through the various settings so I think the stats are ok. Could there be something else faulty causing the short cycling?
4. Would a dirty system cause these symptoms, I'm about to do a flush/clean and inhibit, also plan to fit a fernox TF1?
apologies for all the questions but I know how thorough posters are on this site so want to give as much initial info as possible.
thanks

 

[Chalked]

Getting an oil boiler serviced and running efficiently, is the most important. After that you can turn the room thermostat down a degree or so. Also invest in good draft proofing and insulation.
Depending on your boiler there isn't a perfect temperature, but around 70 degrees in my experience works best for heat, hot water production and efficiency.

 

[Chalked]

Getting an oil boiler serviced and running efficiently, is the most important. After that you can turn the room thermostat down a degree or so. Also invest in good draft proofing and insulation.
Depending on your boiler there isn't a perfect temperature, but around 70 degrees in my experience works best for heat, hot water production and efficiency.

 

[Best]

A room stat to zone the radiators would stop the boiler from cycling so much while the central heating is on.

 

[Balmeadie]

Cheers Best, Would I just leave all the TRVs set on Max and let the Room stat kick in as and when the temp setting that is requires is maintained? Is it easy enough to retrofit one to and old system like this? at the moment everything (DHW, CH temp and timing) is done via the control panel at the boiler which is located in an outhouse.