HOT WATER OVERFLOWING INTO EXPANSION TANK

[HARBISON]

any ideas, we have a classic NF50 gas boiler with pumped hot water & heating with a 3 way valve. Have just found out that that overflow pipe flowing into the small expansion tank is overflowing with hot water.
if i turn the cylinderstat down the pump cuts out & the water stops overflowing. if we turn the heating on with no hot water on the pipe overflows again. any idea may be boiler stat???

 

[gas4you]

Check for a blockage in the cold feed from the f&e tank.

 

[megawatt]

Check the pump.

 

[weareleeds]

If on a fully pumped cross vented "h" system suspect the horizontal piece is blocked with magnetite (try placing a strong magnet on copper pipe). If so you must reconfigure pipework asap or your system will rot & rads will pinhole

 

[kevindgas]

Check for a blockage in the cold feed from the f&e tank.

no it can't be blocked as system is pumping over. it would boil dry if cold feed was blocked
system has crud in it try draining off as much of the water as possible and refilling then add a chemical cleaner like fernox restorer to the system also worth checking the pipework between open vent and cold feed as this may be blocked causing the pumping over

 

[gas4you]

Check for a blockage in the cold feed from the f&e tank.

no it can't be blocked as system is pumping over. it would boil dry if cold feed was blocked
system has crud in it try draining off as much of the water as possible and refilling then add a chemical cleaner like fernox restorer to the system also worth checking the pipework between open vent and cold feed as this may be blocked causing the pumping over

Good point but hopefully if OP cuts the pipe work open to look then he will have seen the cross pipe blocked.

On a 'H' section I find it easier to cut the H out completely and replace

 

[HARBISON]

any ideas, we have a classic NF50 gas boiler with pumped hot water & heating with a 3 way valve. Have just found out that that overflow pipe flowing into the small expansion tank is overflowing with hot water.
if i turn the cylinderstat down the pump cuts out & the water stops overflowing. if we turn the heating on with no hot water on the pipe overflows again. any idea may be boiler stat???

Have looked at the pump & turned it down to low speed (1st setting) from 2nd setting which it was on.this has stopped the water overflowing into the expansion tank. when it was overflowing into the expansion tank the water never overflowed outside
ANY VIEWS ON THE MID POSITION VALVE HAVING A PROBLEM

 

[HARBISON]

Check the pump.[/quote

Have turned pump down from 2nd setting 2000rpm to first setting 1600rrp
this has stopped the overflowing into the expansion tank.
Is it possible that the pump is to big for the system when hot water only is required Pump was changed earlier in the year from a Grundfos to a euramo gold (which we had as a spare) i noticed looking at Grundfos 15/50 that rrp are only 800,1100 &1700rpm on its 3 settings.

 

[gas4you]

You should really be able to have the pump on what ever speed you like and have no pumping over problems.

I think what you have done is take a paracetamol for a broken leg

 

[ScottishGasMan]

higher speed wont necceseraly affect flow from different pumps, a pump with a tiny turbine moving 2500rpm might displace the same volume of water as a much larger pump running at 1000.

I agree with whats been said, I think youve found a cure for the symptoms but not the problem, would suspect cruded up system, needing cleaned out.