potterton statesman flowsure plus-high temp

[disting]

Any help would be gratefully recieved, thanks in advance.
I have a potterton statesman flowsure plus. Its about 5 years old. Has always been a little temperamental, but generally ok, except for a Pump change about 1 year ago.
Current problem is that I noticed the boiler seemed to be running a little hotter than normal, (which I noticed after the Overheat light came on and tripped the overheat button). This happened after runing the shower. the central heating was off, and still is, as the weather is summertime. The boiler has not tripped the overheat button since but:
The gauge for the boiler says temp is 85 degrees (which I am sure is hotter than it used to indicate), and the pressure is constant around 1.5 bar.
I have checked the air pressure in the expansion vessel-0.5 bar, no water coming out of valve and it seems quite light-so no water in it. pressure is holding steady.
I have changed the boiler stat, as, regardless of whether the control knob is set on 1 dot or all the way to the top, temperature on gauge always runs up to 85 degrees. Changing the boiler stat made no difference. Book says with Boiler stat control knob on first dot, temp should be around 55, and 85 at max dots.
Central heating, and DHW all work fine, although they are hot!( Probably would be with boiler running at 85 degrees though!!) no air in boiler or pump or rads now as all bled-steam came out of boiler air vents!! But problem remains
Am I imagining all this, or is the boiler running too hot? Any ideas please. Many thanks.

 

[Boilerman2]

It is quite normal for your Oil fired Combi to run at about 85'c, the boiler is a Thermal Store, which if not at this temperature, will not provide decent hot water, if the water is noticibly hotter at the tap, this is probably due to seasonal changes in the Cold Water inlet temperature

 

[disting]

thanks for the reply. shouldn't the boiler thermostat knob though alter the boiler temp though?, and thus the temperature on the gauge? at the mo its 85 degrees regradless of boiler thermostat knob position and water seems really hot regardless of DHW knob position. cheers

 

[Boilerman2]

It is difficult to explain how an oil fired Combi works, but basically, the hot water is heated by a thermal store (which is Boiler water in a tank separate to the boiler water jacket), this store is controlled by a thermostat, which is hidden away inside the boiler control panel, it is pre-set to 80'c, when this thermostat calls for heat, it switches off the radiators (if they are on) and fires the burner OVERIDING the boiler control thermostat (the one on the boiler front with the adjusting knob) once the store has made 80'c the boiler will switch off, or if central heating is needed, will revert back to heating the radiators. as long as the boiler is not tripping on the Overheat thermostat (which would need you to reset it) you can be sure that nothing is wrong

 

[disting]

great. thanks for the info.
lastly, the pump does not appear to be running continuously. should it??. i seem to remember in the past that it did. could this be the cause of the high temp and thus the steam coming out of the boiler bleed air vents?? strange thing is though, that if the central heating is switched on the rads do get warm...very warm, and so, up to now i have not suspected that this could be the cause of the problem

 

[disting]

pump checked. runs with central heating and hot water demand , otherwise doesn't run (tried another pump and does same things, so back to original)- so if thats normal, then the pump is ok and boiler thermostat change has made no difference either. the temp is still 85 degrees on the gauge, and the hot water tap still gives steaming hot water initially, what would anyone suggest as next thing to look at please.? thankyou

 

[Boilerman2]

Fit a Thermostaic Mixing valve to regulate the hot flow from the boiler (Quality Oil Combis have these as standard!!)