Vokera Linea 730 C/H problem

[kenwalker]

My Vokera Linea 730 Combi Boiler is giving me problems with the central heating. The problem is intermittent but usually at least twice or three times each day.No alterations have been made to the system and the boiler operating pressure is correct. I am neither a plumber nor a C/H engineer but simply a householder who would like to get an idea of what the problem is before taking matters further.

Yesterday for example, I noticed that the radiators were cool despite the rooms still needing heat. Even turning up the thermostatic valves to fully open made no difference, nor did turning up the boiler temperature. On looking at the boiler controls I saw that the temperature indicator was dropping to around 39 degrees and the pipe to the heating was only warm. The boiler then fired up and the temperature started to rise. On reaching about 48 degrees it then flipped to something like 85,72,80 then back to 46, at which point the boiler stopped firing. Switching the boiler off and resetting it made no difference. I then ran a hot water tap and the boiler fired properly and the water temperature was alright. After doing that the boiler settled into a steadier C/H routine of cooling to 55, boiler firing, rising to 68 within a few seconds then jumping to the 80s then back immediately to 63 by which time the firing has stopped. Cooling then started again down to 55 etc.

Everything works fine first thing in the morning and the problems seem to start in the afternoon and evening. When it happens it seems to be running the hot water tap that gets things back into some sense of order.

Any help would be appreciated.

 

[nickso]

does it actually get to the high temps indicated on the display or is the flow pipe still warmish to touch?

i had a similar but not identical episode with a linea a few months ago, that turned out to be a dodgy pump. if its not getting as hot as it indicates then id suspect the primary thermistor.

 

[kenwalker]

Thanks for your reply.The temperature of the pipe gets as high as the 60s but not the 80s so it could be the thermistor.

 

[DP]

Doubt it, faulty thermistor is picked up when boiler does self check at start.

 

[TheGasMan26]

It sounds to me that the Boiler is switching Modes on u, ie-usually it shows ch flow temp but wen u use hw the display will then jump to the hw thermistor, that would also cause your ch to go off as priority is given to hw.
this could be caused by a hw leak somewhere or more likely a dodgy diverter valve, weneva I service a linea I remove the actuator(Diverter motor) head & check pin is moving freely & not leaking from round gland nut, I also carry several diverter valve service kits at all times.
I only say this cos a 40oC jump on display with no middle ground indicates boiler going into hw mode otherwise such a big fast jump in ch flow would likely lead to overheat conditions.

 

[kenwalker]

Primary Thermistor was the problem so thanks to Nickso. The system had been behaving itself pretty well apart from having to reset it a few times, not as hot as it should have been but good enough to get through the cold weather. I was hoping to see an Error Code and eventually one morning it did indicate the Thermistor but a reset got it going again. All the other days no Error came up although the underlying problem was still there. It finally gave up the ghost when the temperature gauge showed 93 degrees although the water was cold and refused to start. (No error code) As I had already bought a Primary Thermistor I fitted it and the system is back to full working order.