right a bit of background first.
6 years ago I bought a house with a recently installed combi boiler from
a tight-fisted landlord.
Whilst under his ownership, he had the vented system boiler & HW
cylinder ripped out and replaced with a sealed combi system boiler due
to a failed gas valve. He did not bother having the existing radiators &
radiator pipework power flushed even though this invalidated his new
The then new boiler is a Glow Worm 30cxi.
His wife then soon divorced him and he sold his house cheaply to me as a
quick sale to pay off his soon to be ex-wife as he wanted to make sure
his wife got as little as possible from him.
Now under my ownership we have suffered from a particular symptom which
is oscillating hot and cold water at the hot water taps, which is worst
at the bath.
This is because the Domestic Hot Water Flat plate heat exchanger (DHW
FPHE) within the boiler keeps on clogging up with magnetite sludge.
This is causing the boiler return water temperature to rise, reducing
Delta T (the temp diff between boiler flow and boiler return) to reduce
making the fan and burner switch off and then switch back on repeatedly
when a Hot tap is opened for a bath.
Its normally a job I can do myself to clear out blockages but the layout
of the boiler is such that you have to remove a 4 inch section of gas
pipe to be able to get the DHW FPHE out for cleaning, and then once back
in, reinstate the 4 inch gas pipe, test the whole house gas pipework for
soundness using a U tube manometer at the gas meter.
Obviously I am not gas safe registered and if I did the work and if
anything went wrong, the insurance company would refuse to accept a
claim. So I get a gas Safe engineer in at 150 quid a time to clean out
the DHW FPHE. this has now happened 2 times in 5 years.
I have now got a Liffe lime beater on the incoming main water and a
Magnaclean on the boiler return pipe for the past 4 years to try and
catch the magnetite from the rads before it gets into the boiler in
order to stop a repetition of the problem.
The radiators and their associated pipework are not blocking up as
obviously all pipework to and from rads are either 22mm or 15mm.
The DHW FPHE has tiny millimetre sized channels so its not surprising
that it gets blocked up in preference to the radiators.
The problem has now reoccurred again for the 3rd time and I now have a
tenant in this house so I need to get the problem sorted once and for
all so I don't end up having to find a new tenant if the current tenant
gets fed up of the problem.
Now what I want to know is if I get a power flush engineer in, will they
be able to power flush the DHW FPHE in-situ by attaching their kit to
the combi boiler's pump? The focus I require is on finally cleaning out
the DHW FPHE as well as the rads.
If the power flusher is connected across a Rad as appears to be the more
usual practice, due to the combi boiler design and its internal diverter
valve, this is not going to flush the DHW FPHE satisfactorily.
If the DHW FPHE has to come out for cleaning, then I will need to find a
Gas Safe registered engineer as well.
Failing that, the nuclear and the most expensive option is to rip out
the 7 year old combi boiler before its natural end of life, power flush
the radiators and then fit a new combi boiler which would solve the
problem once and for all.
I then could clean out the DHW FPHE on the old Glow worm and flog the
boiler onto Ebay perhaps to recoup some of the cost.
Comment welcome on how effective a power flusher is at actually cleaning
the DHW FPHE in combi boilers.....