On 20/06/2019 08:12, S R wrote:

We've had our WB 38CDi GreenStar boiler for about 6 years.

In th elast few months it has developed the folloiwng faults:

1. Hot water not very hot 2. Heaters not very hot.

A local engineer said the issue was a badly clogged up heat
exchanger, but rather than fix/replace that he quoted me a new
boiler.

Well that is could fit in with low output generally. Replacing a main
heat exchanger could cost a significant proportion of the cost of the
boiler. So if there are doubts about other parts of the boiler,
replacement could make sense.

Another engineer suggested the plate exchanger, which was replaced
but theer was no real difference.

The last few weeks, we have started to get a sudden drop in pressure
(hot and cold) after about 1 minute. The pressure is good for teh
first minute, then suddenly drops.

Is this on all taps?

A complication here is that we have have one of those hot water tanks
with immersion heater. After the failed attempt at fixing teh boiler
we switched to teh tank to at least have hot water.

There is something a bit odd here - system configuration wise. You have
what appears to be a Combination boiler - i.e. one that can heat
domestic hot water directly as well as run the heating, but you also
have a hot water cylinder.

This is not an impossible setup, but it is a bit unusual. Sometimes this
is done with say the DHW from the boiler being directed to a single
shower or the kitchen, and then the cylinder HW being used for baths etc.

We normally switch to this during teh winter to stop teh house
getting cold when someone uses teh hot water. But we've switched to
that now as it is the only way to get hot water.

Do you still get the pressure drop?

What kind of cylinder is this? Conventional vented type with a header
tank somewhere? Or an unvented cylinder fed directly from the mains cold
water?


The pressure probelm is the same even when we shut (swith off and
close teh valve to the tank) thyis down.

As I said it was all fine for 6 or so years but now we have these
issues.

I am inclined to think this is boiler related and not something with
the back poressure or pipes.

I think we need a better understanding of the wholes system configuraton
to be able to get further. Like how the DHW of the boiler plays with the
cylinder, and what the valve you make reference to on the cylinder is
doing.

--
Cheers,

John.

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