Highflow Heat Exchanger

[RichardUP]

I need to replace the 'water to water heat exchanger' on a Worcester Highflow 400.

To do this, I am going to remove the 'Pressure relief discharge pipe' and cut the discharge pipe (which leads outside) just below the funnel. This is because the funnel is riveted to the 'support bracket' which shrouds the 'water to water heat exchanger'.

Then, I will remove the five screws (9, 10, 13, 14 & 15) that hold the 'support bracket' to the top and bottom manifolds. This will release the 'support bracket' and the 'water to water heat exchanger' at the same time.

I will then replace the 4 "O" ring seals (at the back of the top and bottom manifolds) and reassemble with the replacement heat exchanger.

I will solder the cut pipe with a capillary joint.

Simple at that!

Or is it ?

 

[kevplumb]

3. Gas to Water Heat Exchanger. See Figs. 17, 36 and 37.
Check that the electricity supply to the appliance is turned off.
Remove the cabinet front panel, place the facia and control box
in the Service Position, lower the expansion vessel and remove
the inner casing cover, as described in Section 14.2 a, b, c and d.
Drain the heating circuit as described in Section 15.2 (a).
Remove the fan, flue hood, combustion chamber cover as
described in Sections 14.2 e, f and g. Remove the Safety
Temperature Limiter thermostat and the CH primary sensor from
the pad as described in Section 15.3.11 and 13.
Remove the left hand fibre insulation pad from the combustion
chamber. Remove the access cover in the left hand side of the
combustion chamber held in position with one screw. Unscrew
the front and rear heat exchanger union connections.
Lift the heat exchanger off the right hand side of the combustion
chamber support and clear of the union connections. Remove
the heat exchanger clear of the inner casing.
CAUTION: There will be a small quantity of water remaining in
the heat exchanger.
Follow the procedure as described in 15.2.
Discard the heat exchanger.
Fit the replacement heat exchanger in the reverse order using
new fibre sealing washers. Ensure the washers are in place and
the heat exchanger correctly aligned.
Tighten the union connections. Refit the access cover to the left
hand side of the combustion chamber and replace the fibre
insulation pad. Refit the combustion chamber cover. Refit the
sensor and thermostat with a layer of heat sink compound. Refer
to wiring diagram Fig. 8. Reassemble the appliance in the reverse
order.

straight out of the book

 

[COG]

The instructions from Kevplumb are for the gas/water so no good but as he sugests get a copy of the instructions ,do not do it as you said unless your a masacist , the only way to do the first one is to do it from the book in brief drain down (don't isolate ch bulkhead valves as they will leak later) remove prv and pipe leading to tundish remove 22mm pipe from top to bottom manifolds then pump,diverter,flow switch complete with pipe then the top brkt and 22mm pipe that goes to the b/manifold (don't get the sol coil wet its not as waterproof as it looks) undo all the grub screws holding the pipes to the manifolds and the clip on the lower one and check the by pass pipe from div valve if its partially blocked check the connections for debri . remove the top manifold first 2 screws one large nut, then the lower and the plate at the same time lifting upover. if any sign of corrosion on the manifold to plate connections replace manifold (not worth the risk if you don't) replace all o rings and lubricate.takes me about 1 hour takes most about 4 hours first time.

 

[kevplumb]

 

[ollski]

yep that is one classic design to do a filter change on these babies.

 

[COG]

Even worse you cant tell if it has a filter fitted untill you try as the early ones had no filters.
Kevplumb just spotted your location ,are you still working around Hartlepool if so who for ?

 

[kevplumb]

me self mate
have worked for gusses and croft bg for a bit but couldn't handle the crap
wimpeys and yuills

 

[Agile]

I need to replace the 'water to water heat exchanger' on a Worcester Highflow 400.

You seem quite sure that you "need" to remove the secondary heat exchanger! Obviously you have your own ideas but I would however question exactly why you would want to do that?

Tony Glazier

 

[jiminblack]

takes me about 1 hour takes most about 4 hours first time.

I must have done at least 20 of these and it still takes me 2 hours. God I'm slow!!

 

[COG]

No your not slow ive just done too many to count mostly in Kevplumb,s patch with all that hard water.

 

[RichardUP]

Yep,

I need to follow those instructions. The 'water to water heat exchanger' is not accessible in the way I had thought.

Thanks for all the replies.

Tony's note leaves me feeling uneasy.

I am of the mind to replace the 'water to water heat exchanger' because that is what fixed it last time. As COG noted there was no filter in the top manifold. Symptoms were; the boiler tripped out when over heating, before that the radiator on the open loop gets hot.

The plates in this heat exchanger seem very closely spaced (make it efficient I suppose) and were blocked with flakes of black stuff. I have cleaned the old one (h/e) out so the water now flows through as easily as the other side. I figure to swap it over.

However, how can I be sure the problem has not been recreated with the clogging of the 'gas to water heat exchanger'. Or does this device allow larger particles to flow through it?

 

[COG]

If you have no primry filter (should have been fitted at last change )or a clear filter the boiler should run faily quiet (no kettlig) in ch mode. removeing the debri from your old heat ex will help but how do you tell if the scale on the walls of the plate are clear ? its not just flow that counts it has to transfer heat eficiantly plus if thit is the second time have you had the system fully cleaned out.

 

[Agile]

My response would be to chemically treat the water and clean the DHW HE remotely!

In any case its the system with the debris that is the problem. DIYers always focus on the DHW HE where the debris collects without thinking of dealing with the cause, the dirty system!

Tony Glazier

 

[RichardUP]

OK,

I have ordered a Magnaclean. Think I should have fitted one years ago.

I have put a bottle of X400 cleaner in the system. Is there a way I can make it work harder on the heat exchangers?

 

[COG]

I try and clean most heat exchangers with a de scaleing machine ,exept for a few such as the 400 with no conection to atach the cleaner to it cant be done remoteley and cant be done in place as its vertical and any serious scale drops down and stops the flow.
If you want to force the cleaners around the heat ex only you can only run the boiler constantley on hot water if you cant aford the gas bill you will have to pull one of the overheat wires off, dont just turn off the gas it will burn out the ign board if its a rsf ok if its bf/of