Hi
I have just moved into a new house and it's always nice inheriting someone else's heating system problems just before the coldest part of the year.
The system is as old as the house (18 years) including the boiler. A Potterton Profile 50e, open vented, fully pumped system with tri-port valve. There are 17 rads (one in the bathroom on a bypass circuit), and a Grundfos 15/60 pump. The vent pipe is connected to an air separator, and the order of the plumbing looks normal (boiler feed, vent, cold water feed, pump, tri port valve).
And here is the problem.
I noticed that the boiler is cycling once the circulating water reaches a "hot" temperature. So it stays on fine from cold, but once warm the boiler will only stay on for 2 mins, then goes off for 1 min, then back on for 2 mins - and cycles this way until the tank stat and room stat are satisfied. When the boiler is in its "cycle off" state, turning the boiler control up a notch fires it back up again, so it appears that the boiler stat is working OK.
I have measured the temp of the water and the drop across the boiler is not great (40-50 return and no more than 60 on the output). It never gets above 60 despite putting the boiler on maximum. I don't leave on max as the one time I did the boiler overheat tripped. But it seems happy on Number 4 (although the boiler itself gets very hot to the touch)
I recently noticed that one of the rads was cold in the middle. Although I have a invoice showing the system was powerflushed a year ago, I took that rad off and got a lot of muck out of it. It now gets hot throughout.
I have now also noticed that when both HW and CH are on, there is a constant trickle of water from the vent pipe into the f&e tank (I have tested this with the boiler off, just the pumps and valve operating and it pumps over regardless of whether the boiler is on or not). Note, if only HW or CH is selected then there is no pump over.
I am guessing 60 is too cool for the boiler output when the boiler is on No4, so there is not enough heat exchange going on in the boiler (sludge/scale in the exchanger?) and this could cause the cycling, but reading these forums indicates that pumping over is normally caused by a blockage between the vent pipe and the pump? (or could I gave both problems) Can an Air Separator go faulty or get blocked? It is a simple copper can type. I have tried putting a magnet on the pipes around that area (as advised) but can't get it interested.
I have just half drained the system and put in two bottles of Fernox F3 and topped it back up again, so will leave it for a week, but if anyone had any thoughts on the problem I would appreciate it (as I am not hopeful with the F3). BTW the f&e tank had a nice coating of brown sludge on the bottom which I left undisturbed as much as I could.
Should I expect to have to get it powerflushed after one year (or does it indicate that the powerflush didn't clear it out properly?
its worth adding that the rads do all get hot and I do get hot water. The house could be a bit quicker at warming up but its not too bad - I am more concerned about the long term damage that could be going on (eg stress on the boiler when cycling)
Sorry for long story but have noticed a lot of questions get answered with questions so I thought I would try and get everything covered first off
Thanks
Dave
I have just moved into a new house and it's always nice inheriting someone else's heating system problems just before the coldest part of the year.
The system is as old as the house (18 years) including the boiler. A Potterton Profile 50e, open vented, fully pumped system with tri-port valve. There are 17 rads (one in the bathroom on a bypass circuit), and a Grundfos 15/60 pump. The vent pipe is connected to an air separator, and the order of the plumbing looks normal (boiler feed, vent, cold water feed, pump, tri port valve).
And here is the problem.
I noticed that the boiler is cycling once the circulating water reaches a "hot" temperature. So it stays on fine from cold, but once warm the boiler will only stay on for 2 mins, then goes off for 1 min, then back on for 2 mins - and cycles this way until the tank stat and room stat are satisfied. When the boiler is in its "cycle off" state, turning the boiler control up a notch fires it back up again, so it appears that the boiler stat is working OK.
I have measured the temp of the water and the drop across the boiler is not great (40-50 return and no more than 60 on the output). It never gets above 60 despite putting the boiler on maximum. I don't leave on max as the one time I did the boiler overheat tripped. But it seems happy on Number 4 (although the boiler itself gets very hot to the touch)
I recently noticed that one of the rads was cold in the middle. Although I have a invoice showing the system was powerflushed a year ago, I took that rad off and got a lot of muck out of it. It now gets hot throughout.
I have now also noticed that when both HW and CH are on, there is a constant trickle of water from the vent pipe into the f&e tank (I have tested this with the boiler off, just the pumps and valve operating and it pumps over regardless of whether the boiler is on or not). Note, if only HW or CH is selected then there is no pump over.
I am guessing 60 is too cool for the boiler output when the boiler is on No4, so there is not enough heat exchange going on in the boiler (sludge/scale in the exchanger?) and this could cause the cycling, but reading these forums indicates that pumping over is normally caused by a blockage between the vent pipe and the pump? (or could I gave both problems) Can an Air Separator go faulty or get blocked? It is a simple copper can type. I have tried putting a magnet on the pipes around that area (as advised) but can't get it interested.
I have just half drained the system and put in two bottles of Fernox F3 and topped it back up again, so will leave it for a week, but if anyone had any thoughts on the problem I would appreciate it (as I am not hopeful with the F3). BTW the f&e tank had a nice coating of brown sludge on the bottom which I left undisturbed as much as I could.
Should I expect to have to get it powerflushed after one year (or does it indicate that the powerflush didn't clear it out properly?
its worth adding that the rads do all get hot and I do get hot water. The house could be a bit quicker at warming up but its not too bad - I am more concerned about the long term damage that could be going on (eg stress on the boiler when cycling)
Sorry for long story but have noticed a lot of questions get answered with questions so I thought I would try and get everything covered first off
Thanks
Dave