Central Heating Review, Address Removed, Kings Clipstone, Nottinghamshire
The property is a large
detached dwelling built in the Spring of 2003. The Central Heating System had
apparently been running satisfactorily until approx Christmas 2005 when it was
noticed that the radiator in the Breakfast Room was not heating up. The occupant
tried to remedy the problem himself by bleeding the radiator through the
combined radiator/drain valve and by opening fully the Gate Valves in the
Cylinder cupboard. It was also noticed that the radiators in the Bathroom and
Landing were heating up intermittently.
In the Spring of 2006 a
plumber was called who balanced the system and identified that the Circulating
Pump required replacing with a higher capacity unit which he said he would call
back and replace at a later date. Unfortunately that plumber did not return and
after several months of waiting the occupant contacted Ball and Sons.
The property is a modern
brick built dwelling which consists, on the ground floor, Lounge/Dining Room,
Kitchen/Breakfast Room, Hallway, Utility Room and Cloak Room, and on the first
floor, 5 bedrooms with 2 ensuites, one with shower and one with bath, a Family
Bathroom and a Landing.
The property has a total
of 16 Radiators with a total output of 10.4 Kilowatts, all pipework is copper
with the terminal heating pipework being 10mm microbore, a hot water storage
cylinder of 210 litres capacity all of which is served by a Potterton Suprima
50L wall mounted boiler situated in the integral garage.
In recent weeks it was
decided to replace the Circulating Pump, which was 5m head capacity, with a
higher capacity 6m head unit. A Grundfos Alpha 15-60 variable speed pump was
fitted as it was thought the extra capacity would overcome the circulation
After fitting the pump it
would appear that the increase in pump performance has revealed more circulation
problems including reverse circulation which caused the radiator circuit to heat
up when the system was only calling for hot water. After eliminating any
possibility of defects in the zone valves a more detailed examination of the
system layout was undertaken. This examination revealed several flaws in the
The system is piped in the
“S Plan” configuration where separate zone valves control the hot water and
central heating; these are independently controlled by the system programmer and
thermostats. When the system calls for hot water the boiler fires and the hot
water zone valve opens allowing heated primary water to circulate through the
cylinder coil heating up the domestic hot water. The same occurs with a call for
heating, the boiler fires and the zone valve for the radiators opens allowing
heated primary water to circulate through the radiators. When hot water and
heating are both satisfied the zone valves close, at this time there is excess
heated water in the boiler and in order to safely dissipate this heat a by-pass
circuit is used which allows the heated primary water to flow through a circuit
of pipework until it cools.
requirements for this system are supplied by Potterton, on Page 11 is the layout
plan. The Potterton Suprima 30L – 100L Installation and Service
Instructions Pages 9 –11 are produced as Document One
requirements are that the order of flow connection immediately after the
circulating pump are
This installation plan
follows the Thee Tee Rule which governs the order of connection of various
features of the system.
An explanation of this
rule is given in Document Two which is an extract entitled 1.8 Central
Heating System Layout from the book by John Reginald – Central Heating
Fault Finding and Repair.
Images of this
installation and a schematic are produced as:-
Image One – Zone
Image Two – Return
Image Three – Final
In this installation the
order of flow connection is (Image One)
This reveals two major
faults, firstly the by-pass is in the wrong place and secondly the Radiators and
DHW Cylinder connections are reversed thus the Three Tee Rule has been broken.
Image One – Zone
requirements for the return connections immediately before the boiler are
In this layout the order
of return connection are (Image Two)
Image Two – Return
This reveals a further
major fault in that the Radiators and DHW Cylinder connections are reversed
again breaking the Three Tee Rule.
The consequence of
breaking the Three Tee Rule is Reverse Circulation.
A full explanation of this
condition is given in Document Three -
a further extract from Reginald’s book entitled 1.9 Central Heating
– Reverse Circulation
I also refer to the Plumbing
Engineering Services Design Guide issued by the Institute of Plumbing and
Heating Engineering (IPHE) which states at Page 59 Piping Installation Item 10.
“Always connect the DHW cylinder primary return as the last connection on the
return pipe to the boiler, after any heating return connections to avoid reverse
circulation problems” This extract is produced as Document Four.
requirements for the by-pass is listed on Page 9 of the Potterton Installation
Instructions (Document One) and requires the fitting of a Lock-shield valve
adjusted to the required flow rate. A Lock-shield valve is a valve that is
adjusted by the plumber and then locked to prevent interference with the setting
by the householder.
In this installation a
Gate Valve has been used which may well have been correctly adjusted on
installation but because as it is a manually operated valve the householder was
able to fully open it in his attempts to solve the circulation problems. As an
absolute minimum the wheeled head of the Gate Valve should have been removed
after setting as this would have prevented any later intereference. Better still
would have been the fitting of an Automatic By-pass Valve which can be set to a
specific flow rate and are not very expensive (about £30). The IPHE Plumbing
Engineering Services Design Guide (Document Four) suggests that an Automatic
By-pass Valve should be used to avoid boiler inefficiency.
The by-pass should also
come off the pipework at right angles so that flow is only directed through it
when the zone valves are closed, at present the position is more or less
straight from pump to by-pass and consequently unrestricted flow is going
straight through it.
A further flaw in the
pipework was noted at the last connection from the Radiators to the Radiator
Return Pipe which is situated in a void under the Cylinder Cupboard.
An image of this pipe
junction is shown in Image Three.
Three – Final Radiator Return
This connection consists
of a 22mm Tee with the direction of the return coming in from the left, the
return route is then upward through the top connection, the right connection is
reduced from 22mm to 10mm and connected to a return pipe from a radiator or
radiators. The direction from this return is coming in from the right. It is
difficult to establish precisely which radiator this return serves although the
adjacent room is Bedroom 4 and this is an obvious choice however no major
problems have arisen with this radiator.
Due to the inadequacies of
the system layout major circulation problems have arisen.
When the Radiator Circuit
only is activated a significant amount of primary water is going through the
by-pass directly into the return to the boiler. This is highly inefficient as
none of this water is reaching any radiators. It is also possible that some of
this water is finding it’s way down the radiator return in a reverse
direction, the result being that the pump is then working against itself.
The final return from the
Radiator into the tee directly opposite to the direction of flow of the other
Radiators is a major cause for concern; the amount of water getting through this
fitting into the return can only be minimal at best. This will cause significant
impairment of the circulation to whichever of the radiators is served by that
When the Hot Water Circuit
only is activated the combined effect of the open and straight by-pass and the
return from the Cylinder being before the Radiators results in reverse
circulation to the whole Radiator Circuit.
When both circuits are
open all the above circulation problems are combined.
installation instructions have not been followed in this system layout and
circulation problems have arisen as a result.
In addition extra fuel
will have been used due to system inefficiency and the extra strain placed upon
Additional expense has
also been incurred for example the fitting of a higher capacity pump.
Enclosed is my estimate
for the required remedial work to the cylinder cupboard pipework.
Update March 2007
The builders of the property paid for the remedial work to the pipework in the cylinder cupboard and the problem was solved.
The by-pass and valve order was rectified and a swept tee used on the DHW connection into the return.
The dodgy microbore return was capped off at the tee against the flow and re-connected higher up the return.