Changed pump now overflowing!

[medic999]

my 10 year old grundfos 15 50 central heating pump has got noisy recently so i changed if for a new one today and all went rather well! I put the heating on and the house warmed up really quickly.
i could hear running water so went into the loft to investigate and noticed hot water running out through a vent pipe into the top of the central heating tank in the loft. each time i put the boiler on for either the heating or to heat some water for the immersion tank hot water overflows. the tank in the loft is hot too touch and full of hot water.

i have tried turning down the thermostat on the boiler with no effect.
the new grundfos 15 50 is on the lowest setting (1)
both valves that i closed to change the pump have been opened up again.
my boiler is a glow worm.

I have taken a picture which can be seen here - http://www.diynot.com/network/medic999/albums/

my knowledge on this sort of thing is very limited so would appreciate any advice (i am quite good at medicine so would be happy to give my opinion on any coughs or colds you may have)!

 

[gassafeengineer]

did you put it on with the arrow pointing the same way as the old?

 

[tamz]

Turn the pump speed down

 

[gassafeengineer]

Turn the pump speed down

hes already said its on one which to my knowledge is the lowest it goes

 

[Hugh Jaleak]

Blockage somewhere? Is there an air seperator fitted? (Round 'can' type thing, before the pump.)

 

[tamz]

Turn the pump speed down

hes already said its on one which to my knowledge is the lowest it goes

So he did, never read it right

Either pump on wrong way or valve not opened fully. Can't see it being a blockage if it was ok the day before

 

[medic999]

did you put it on with the arrow pointing the same way as the old?

I cheated a little a left the back in situ and only replaced the pump head

 

[medic999]

Blockage somewhere? Is there an air seperator fitted? (Round 'can' type thing, before the pump.)

not that i can see.

if i close the gate valve that comes from the tank in the loft into the pipework the water stops overflowing the other way back into the top of the tank in the loft

 

[glasgowgas]

would be checking those pump valves are definetly open

 

[gassafeengineer]

when turning valves anti clockwise do they come to a firm stop?

 

[medic999]

would be checking those pump valves are definetly open

just double checked. closed them both down and listened for the noise to change on the pump then opened them both back up and now nice and quiet but still overflowing!

 

[medic999]

when turning valves anti clockwise do they come to a firm stop?

yes

 

[gassafeengineer]

new pump definately 15-50 not 15-60

 

[glasgowgas]

check where cold feed enters system with a magnet, if it sticks you have a blockage

 

[medic999]

check where cold feed enters system with a magnet, if it sticks you have a blockage

What do you mean by enters system? is this the pipe from the tank in the loft?