Dear Jeff, Our boiler is now seriously faulty - it cuts out pretty much every day, sometimes more than once. Sometimes it shows the F22 error message; sometimes it simply doesn't fire up even though the temperature is showing around 30 degrees. On the other hand, once I restart it, it works fine and the house/water get nice and hot. So it would seem ridiculous to replace the whole thing for what is presumably a fault in the control system. What would you advise? Cheers
It always f22 or sometimes f75?
I've never seen f75
F22 is triggered by flow temperature rising too quickly, cause by poor circulation. Poor circulation could be: Problems with motorised valve (but didn't I leave hot water one permanently open to test this ) Rusty corroded heat exchanger. (I think Vaillant don't cover this in that price) Sludge in system - could flush it, but need to do it to see if it'd work. If it turns on and does f22 then you reset it, it may stay on the second time as the initial heat helps the circulation. D
"If it turns on and does f22 then you reset it, it may stay on the second time as the initial heat helps the circulation"
Yes, I think it does tend to stay on after I've reset it once. " Poor circulation could be: Problems with motorised valve (but didn't I leave hot water one permanently open to test this ) Rusty corroded heat exchanger. Sludge in system - could flush it, but need to do it to see if it'd work." Do you think it would be worth examining the heat exchanger, as you thought the main circulation wasn't sludgy? Or would that cost almost as much as installing a new boiler? Cheers
So based on that, second time round it gets there, if stat was a bit more patient it'd be ok for now. So it seems like poor circulation by pass valve and pump already been changed, one motorised valve open so if there eliminated leaves: Heat exchanger or sludge in system which would require a flush. Problem is I'm always a bit apprehensive to say let's go and flush it cause we don't 100% know what the circulation problem is. Equally no point changing the boiler and having the same problem! If you change the boiler the system is flushed and you get a new heat exchanger. Off the top of my head (which is sometimes better than thinking it through). Flush it and if anything that might throw light on any other problems in the process.
Are there any more sensors it might be worth changing, eg is there one for the pressure? After that, is there a motherboard one could replace? It feels to me like a problem in the control hardware (or software) rather than in the crude mechanics. (I think we may have had the system flushed not more than a couple of years ago). Could I be right?
Could change the thermo stat but vailliant are quite sure this rarely has a problem. Also if the stat failed I would expect f22 all day long like wise with the PCB. Intermittent problems are usually mechanical, control/electric are usually constant constant.
So I guess I disagree and think it is a mechanical problem.
If you want to eliminate controls change stat and then PCB, PCB's can be expensive are always non return able and even though it's an old boiler I might normally suggest a reconditioned part if it's expensive but not the re conditioned PCB's as they do often have problems.
This problem was actually resolved by changing the stats. In this case there where two individual thermo stats both potentially triggering an f22 fault code. Once the stats were changed no more f22 fault were recorded.