Fitting a water to water heat exchanger to a cdi28 combi

joeb99 · 5 Jan 2010

Hi,

I bought the exchanger, it has 6 washers;

1 fiber washer

orings:
1 large,
2 medium,
1 small,
1 very slightly smaller.

Where do the two small o-rings go? When i take off the old unit the other rings will be apparent, but i cant figure out why there is a small ring, and a very slightly smaller oring. (unless they put in the wrong ones?)

Also, do you grease the joints when assembling?

namsag · 5 Jan 2010

You will see where they go on removal, dont be tempted to think the ones on there look ok as they will pi55 out if not changed

kevplumb · 5 Jan 2010

joeb99 · 5 Jan 2010

ok thanks. But the two small ones are very slightly different sizes. Not sure why?

nickso · 5 Jan 2010

it doesnt matter, they can both go on either connection.

joeb99 · 8 Jan 2010

HI,

I changed the heat exchanger and the safety overflow pressure valve.

The heat exchanger was fairly straight forward, no problems. Didnt grease the o-rings (was i suposed to?)

Had a slight leak from a pipe behind the differential pressure switch (the white disc with 2 flexible pipes), so tightened the nut and its all ok.

So now, i have no hot water or central heating!!

I pressured up the boiler to 1.5 bar, bleeded the rads.

Turn on the boiler, turn on hot tap, burner fires up, 3 secs later, gas turns off.

A bit later on, its indicating a overheating fault. (tap and radheater lights flashing together)

The heat exchanger does not get hot, the pump gets very hot, so the water is heating, but doesnt seem to get into the heat exchanger. Cant see any valves on the exchanger, and the boiler used to work before i removed and replaced the exchanger.

Only parts i touched was the water/water exchanger and the filling loop.

Any ideas? Maybe the exchanger has an air lock inside it?

Misses has gone to a b&b with the baby because we now have no hot water or heating!

kevindgas · 8 Jan 2010

is the air release valve cap open on top of the boiler?

joeb99 · 8 Jan 2010

There is a air release i think on top, it looks like a air valve thats fitted to a car poking out of the case, there is no cap on the screw thread.

joeb99 · 8 Jan 2010

Is there a way to bleed it if this valve is broken? How can i check the valve?

kitch0978 · 8 Jan 2010

try bleed some air out of the pump......did you close isolation valves on boiler whilst changing heat ex? if so are they now open...?

joeb99 · 8 Jan 2010

No i bleeded down the whole system becuase the isolators leak for a week if you touch them

best to avoid that.

Blead the pump, all working now.

THANKS EVERYONE !!

Will get corgi / gas safe to change the auto vent next time the boiler is serviced as its in the combustion chamber.

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Fitting a water to water heat exchanger to a cdi28 combi

namsag

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