Happy New Year to all.
I need advice re: my Vaillant Sine 18.
Hopefully there are still some of the old Bunny brigade reading this forum.
Yes, the boiler is donkeys’ years old but it has served me well and I appreciate its superb engineering. Having said that, I will be replacing it in the summer, simply because it is difficult to get it serviced and spares are becoming more rare than hens’ teeth.
It was last properly serviced three years ago, although by a young man who I suspect had never seen one before. Initially no problems but then it started to develop a problem with the DHW, in that it would not get very hot and was simultaneously warming up the heating circuit. Referring to this forum, I concluded that the wax-stat in the diverter needed replacing. Luckily, I had sourced a new wax-stat as a precaution a few years ago, before they completely disappeared. I did not replace it immediately for fear of causing leaks etc; and the boiler soldiered on. Then last month, intermittently it started to fail to fire-up when requested. Following some investigation, I found the differential pressure valve was failing so the gas valve was not opening. I also noticed that the boiler pressure was dropping more quickly than previously and then found that the AAV was leaking like a sieve.
I replaced the differential pressure valve, the wax-stat and the AAV. I evacuated and re-pressurised the expansion vessel to the recommended pressure and the boiler returned to what I initially thought was normal working: central heating fine, DHW better than ever. But then I noticed that in central heating mode, the boiler was constantly firing in 15 second bursts and then going out completely rather than modulating (if that is the correct term) as I am sure it used to. Checking the solenoid terminals showed a constant 14.9v whether firing or not (which is surely not right?). Switching the DHW preheat switch on or off makes no difference. Detaching the NTC wire makes no difference. Adjusting the thermostat setting makes no difference. I should mention that my system has no room stat and all radiators have TRVs.
I suppose the problem could be the electronic PCB, although that was replaced about six years ago. Could it be the thermostat? Does the new wax-stat mean that the micro-switches on top of the diverter need resetting? i.e. could it be operating the central heating as a sequence of DHW preheat cycles? This is all guesswork on my part but I am hoping that someone can help me keep the old girl running properly for the rest of the winter until she is pensioned off in the summer.
Thanks in advance.
Mike
I need advice re: my Vaillant Sine 18.
Hopefully there are still some of the old Bunny brigade reading this forum.
Yes, the boiler is donkeys’ years old but it has served me well and I appreciate its superb engineering. Having said that, I will be replacing it in the summer, simply because it is difficult to get it serviced and spares are becoming more rare than hens’ teeth.
It was last properly serviced three years ago, although by a young man who I suspect had never seen one before. Initially no problems but then it started to develop a problem with the DHW, in that it would not get very hot and was simultaneously warming up the heating circuit. Referring to this forum, I concluded that the wax-stat in the diverter needed replacing. Luckily, I had sourced a new wax-stat as a precaution a few years ago, before they completely disappeared. I did not replace it immediately for fear of causing leaks etc; and the boiler soldiered on. Then last month, intermittently it started to fail to fire-up when requested. Following some investigation, I found the differential pressure valve was failing so the gas valve was not opening. I also noticed that the boiler pressure was dropping more quickly than previously and then found that the AAV was leaking like a sieve.
I replaced the differential pressure valve, the wax-stat and the AAV. I evacuated and re-pressurised the expansion vessel to the recommended pressure and the boiler returned to what I initially thought was normal working: central heating fine, DHW better than ever. But then I noticed that in central heating mode, the boiler was constantly firing in 15 second bursts and then going out completely rather than modulating (if that is the correct term) as I am sure it used to. Checking the solenoid terminals showed a constant 14.9v whether firing or not (which is surely not right?). Switching the DHW preheat switch on or off makes no difference. Detaching the NTC wire makes no difference. Adjusting the thermostat setting makes no difference. I should mention that my system has no room stat and all radiators have TRVs.
I suppose the problem could be the electronic PCB, although that was replaced about six years ago. Could it be the thermostat? Does the new wax-stat mean that the micro-switches on top of the diverter need resetting? i.e. could it be operating the central heating as a sequence of DHW preheat cycles? This is all guesswork on my part but I am hoping that someone can help me keep the old girl running properly for the rest of the winter until she is pensioned off in the summer.
Thanks in advance.
Mike