This is because all combination boilers have to warm the water up from cold
as it is running and this takes a lot of energy, this is limited to gas supply
so all manufactures limit the boilers to about 30KW(input & 28 output)
and this is just enough to
lift the water temperature up to 60deg C if water flow is slowed down to about 1.5 Gall/min.
most combination boilers can only raise the cold water temperature by 35C unless
you slow the tap down. a 24KW boiler will not be as good
this is why combination boilers are only recommended for smaller homes with a
low hot water usage and defiantly not for homes with more than one bathroom
Combination boilers are designed to be used on sealed systems that is they
have an expansion vessel built in. but if fitting one onto a system with old
radiators then it is sometimes advisable to fit an open vented expansion tank so the extra pressure
can not damage the radiators or valves, but nearly all new combination boilers
will only work on a
The most common reason is corrosion in the system, this can be caused my the
system not being flushed out correctly when new or being wrongly installed, but it
takes quite a few years for the first radiator to leak. the system needs
checking over, if any design fault is found it needs rectifying then flushing out and
inhibitor added
Technically he is correct providing every radiator has a TRV fitted and a
By-Pass is incorporated but This will increases the stress on the boiler and will
increase running cost's and will have a shorter lifespan. the best systems have
a room stat fitted near the main living area and since April 2002 is part of the
Building regulations (part L) so is now mandatory. TRV's should still be fitted in
bedrooms and south facing rooms, room thermostats allow the boiler to rest when the
house is warm and will reduce ware & tear also
reducing fuel bills and reduce the CO2 emissions therefore reducing the
greenhouse effect
The best control for combination boilers is a programmable room thermostat
then no other time clock is needed
Usually this refers to the how the gas burner operates. Some boilers are
fully modulating which means the gas pressure is controlled electronically
keeping the output constant, Other boilers are semi modulating which usually
means the boiler has a full rate and a low rate and alternates between the two,
A semi modulating combination boiler would result in a non thermostatic shower varying
in temperature, also this could be caused if you have poor water pressure or
someone else drawing water or the flushing of a toilet
One off My Radiators is cold ?
When you bleed the radiator did water come out?
If not & if you have a sealed system is the pressure gauge at 1 Bar?
Try turning the Radiator valve fully open (anticlockwise ) & on
the opposite side there should be a cap that you can't turn, remove this cap
& using a small spanner make sure that the valve spindle is fully open
(anticlockwise )
If still no heat try turning all the remaining radiators off and then put
the heating on only
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The boiler pressure should be at 1 bar, which will need topping up manually
by the fill loop
This is usually under the boiler and may have one or two taps on it and
should be a flexible pipe
Fill to one bar, Bleed all the radiators and Refill to one Bar
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I believe that the fully pumped system is the most reliable and versatile especially
when fitted with an unvented cylinder (water pressure permitting,) and either
a Low water content boiler or a System Boiler
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Plum is a term for lead so plumbers originally worked with lead putty &
paint, so you would call a plumber to fit windows or the lead piping for the
water, but over the years plumbers have concentrated on the plumbing of water
and the drains and they take plumbing qualifications
Heating engineers have always concentrated on heating systems both design
and maintenance,
Lead can no longer be used so both plumbers and heating engineers use
copper & plastic and because both types of installation work are now very similar
the public think plumbers are Gas Experts especially since the demise as what
was known as The gas board
since the invention of the combination boiler which needs virtually no design
as everything is built in then a lot of plumbers are now installing boilers
(mostly Combination boilers) but unfortunately quite a few still only have
there plumbing qualifications plus a basic CORGI registration which is why a
lot of plumbers will install a boiler but not maintain it and is also why they
tend to recommend Combination boilers
A Gas heating engineer should be able to install any type of system and
solve any problem on a Ch system but will not fit bathroom suites or work on drains
so there are 2 distinct trades that have merged together over the years and
there are good & bad plumbers as there are good and bad heating engineers
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How can I work out my radiator sizes
There are 2 links to heat loss programs from my Useful site links
page also look at the radiator page for the best positioning
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Do the 2002 Building Regs. apply to my
system?
These Building regulations
apply to all new systems, and if you change the boiler or hot water cylinder
and adding radiators to a system and is for your own benefit as not only will
it reduce the CO2 emissions they will also reduce your fuel bills
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How do I connect a room stat
in to my Ch system
Most of the common wiring diagrams are on the web site but basically you interrupt
the Heating on wire from the timer. Or if it is a fully pumped system it is
the wire controlling the opining of the valve in the wiring center, if it is
oh the "Y" plan type then its the white wire but if it is the
"S" plan type it is the Brown wire on the heating Motorised valve
but there are so many types of systems a may need an electrician r heating
engineer
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Can I fit a new fire front onto my Back Boiler?
some manufactures do make replacement fire fronts but they are quite
expensive and there is not a lot of choice, the best solution is to fit a low
water content boiler in a new location and convert the system to fully pumped
if necessary then you can have any fire you want, the CH system will use less
gas and providing the new fire is less than 7KW input then you will not need
the air vent in the room,
you must never try and use a back boiler without the fire front
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I have been recommended an unvented cylinder,
what is it?
An unvented cylinder is like a normal indirect cylinder but it works on
mains water pressure so will provide hot water at the same flow rate as your
cold, all the manufactures are producing these now and most of the
better builders are installing these systems in there new housing, they are
quite big but you do not need a header tank, they are brilliant for modern
mixer & Body showers
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What is a power shower?
A power shower can only be used on a normal vented hot water cylinder as
these are Powered by an electric pump to increase the water flow to the shower
head, so these must not be used with a combination boiler or unvented
cylinder as these are more powerful anyway because of the mains water pressure,
if you can get the header tank 2m above the shower head then will create
enough water pressure for a good mixer shower without buying a power shower
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Have I got sludge in my system?
Sludge is only
formed if there is a problem with the system
If you get a
magnet and touch it to the copper pipes there should not be any attraction, if
you find that the magnet is attracted to the copper pipes then you have
magnetite in the system, the most likely place is the point that the cold feed
enters the system
If you do have
sludge then this is usually caused by either the system was never flushed out
correctly or it has been piped up incorrectly as on most fully pumped systems
the cold feed should enter the system next to the and as close as possible to
the Expansion pipe
the
magnetite is actually rust from the radiators that are rotting from the inside
and will eventually leak if the problem is ignored
also
if you have this problem then the radiators need venting regularly
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I Have been told my system needs a Power
flush Why?
This
is the latest gimmick, probably less that 1 in 10 systems actually need a
power flush but a lot of people are selling them because it is easy
money. it is basically a big pump in a bucket that circulates water
though the system with chemicals added, the only time it is possible that a
system needs a Power flush is on a fully pumped system with sludge in the
system and even then the cause of the sludge needs finding first,
if a system is fitted correctly and was flushed out correctly when new then
the water in the system will stay clean providing you do not have a water
leak, sealed systems should never need a power flush, a typical
charge is about £500 yet the chemicals cost less the £50 so the rest is
profit. when you replace a boiler the system must be flushed anyway as per the
manufactures instructions but some firms sell a power flush at the same time
as a boiler change so you end up paying twice for something they should be
doing as part of the installation
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My boiler keeps getting up to 3 Bar and letting
water out why?
The pressure should only be at 1 Bar as the safety valve
will open at 3 bar for safety as that is its job.
If the pressure gauge is at 1 bar when the system is cold then it rises to 3
Bar when it is hot then it is almost certainly the expansion vessel that needs
re-charging with air as it should take up the expanded water when heated
The expansion vessel is at the back on most boilers but they are usually Red
in color so are easy to find
With the system off & empty of water locate the Shredder valve on the
expansion vessel, remove the dust cap and using a Foot Pump put the air
pressure up to 10PSI ( you may need to let some more water out of the safety
valve by twisting it) replace the dust cap, shut the safety valve and refill
the system to 1 bar
If it still is getting up to 3 bar then either it is
getting water from the fill loop of the water to water heat exchanger or the
pipe to the expansion vessel is blocked
This is usually the result of a blocked cold feed (Sludge) on a
fully pumped system, or the Cold feed and expansion pipes being too far
apart
On a fully pumped system the Expansion pipe and cold feed
pipe should be as close together as possible on the primary flow before the pump
or connected directly back to the boiler
alternatively the boiler stat may not be working so the
water boils, this is more likely on a gravity Hw system
