Cool-hot water.

[stani]

I have been out to an Ideal Classic, where the customer is complaining of cool-hot water, flow from boiler through an S plan to cylinder is 71c, return is 54c but hot water won't get much above 48c.
cylinder stat set at 65c it is working, pump and valve both running,
it is in Manchester so no hard water/calcification problems,
anybody had a similar problem.

 

[Ermintrude]

Have u opened cylinder balancing valve ( on bottom outlet) what is temp drop across cylinder coil? If low possibly an issue with heat transfer but would think that if left on long enough water would reach thermal equilibrium with heating water. When in mid position are A and B same temp as C? If not possibly prob with balancing or bypass open too far??

 

[stani]

There is no cylinder balancing valve, client explains boiler been on at least 12-14 hours, there is no A-B it's 2 x 2 port valves.

 

[Ermintrude]

Crank all rads down! Is flow across both zv same temp when both activated? Is cylinder F&R same temp or is cyl (when cold) taking heat from primary?

 

[stani]

Sorry just read 1st post, the flow through the cylinder is 71c and the return from the cylinder is 54c, so there is a 17 c drop but the dhw is just not getting red hot.

 

[Ermintrude]

Is cylinder piped correctly? What is temp of cylinder at hot draw off ? U would expect water to be close to 65c then if dumping 17c from 75? It's not a 5000l cylinder on a 12kw boiler?

 

[stani]

No just a 900 x 450, pump is in the same cupboard, was wondering wether impeller knacked, or wether coil gunged up and not allowing proper circulation.

 

[julesverne]

sludged up coil ?

 

[Ermintrude]

Might be sludge, but getting a reasonable temp drop, add some 800 and then flush out a week later.