Combi - hot water issues.......yaaawn!!

[Bunker]

I have a customer with a combi (Grant - oil) and he complains of low HW temp. He has no softener etc (fool!). Ive measure the primaries on the heat exchanger at 68 degrees in and 60 out and the HW out is 26 degrees. Obviously I cry 'Scale' as usual.
This post is about me learning more about that. Where is the scale? The flow seems ok so if it was in the primaries then surely the secondary would absorb more of the 68 degree heat. If the secondaries are scaled up, surely the flow would be reduced.
Any schooling would be welcome.
Thanks

 

[Plumb Ugly]

Does it have a blending valve?

 

[Bunker]

Yes, I checked that when I was there last and its set to max heat (as usual).

 

[Billy Bob Bob]

are you measuring on a plate heat exchanger?

 

[Bunker]

Yes, the primaries in and out of it and the HW out.

 

[Plumb Ugly]

Had a couple of faulty ones especially in hard water areas that wouldn't give proper hot water, managed to sort a couple by cleaning them out worth a shot i guess

 

[Bunker]

cleaned out the heat exchanger? I often wonder about wether flushing through with fernox would work?

 

[Billy Bob Bob]

run the hot water tap without the heating being on so the ch flow is stone cold if it gets hot or the boiler overheats your plates blocked,if not look at the blending valve or if fitted measure the resistance of the dhw thermistor and compare it to mi,s

 

[SimonG]

I've had more dodgy mixing valves than heat ex's but then I live in a sof****er area. Only heat ex's that have had to be changed have been off of springs or bore holes.

 

[SimonG]

Whey hey, works with soft water as well as ho****er

 

[Plumb Ugly]

No sorry i meant the blending valve but you could try cleaning the plate heat exchanger if you think the system may be dirty. Iv done this a few times rather than buying a new one takes a bit of time running it under the tap and tapping it until black scale stops falling out of it but I was surprised how well it has worked! Hope thats some help

 

[Billy Bob Bob]

Whey hey, works with soft water as well as ho****er

its the bit in the middle causing all the trouble as usual

 

[Billy Bob Bob]

No sorry i meant the blending valve but you could try cleaning the plate heat exchanger if you think the system may be dirty. Iv done this a few times rather than buying a new one takes a bit of time running it under the tap and tapping it until black scale stops falling out of it but I was surprised how well it has worked! Hope thats some help

cleaning does work,not always if its ingrained crud but worth a shot

 

[lame plumber]

Is water pressure over 8 bar (prvneeded) or has the flow restrictor been removed allowing over 15l/min flow rate

(why isnt this in oil/solid fuel section) :29: