2 port Vs 3 port central heating valves

[EMC]

I am just about to embark on upgrading my old oil fired gravity hot water /
pumped central heating system to a gas fired fully pumped system and am
unsure what arrangement of valves to use. What are the advantages /
disadvantages of using a 3 port valve instead of two 2 port valves to
control a fully pumped hot water and (single zone ) central heating system?

 

[IMM]

I am just about to embark on upgrading
my old oil fired gravity hot water /
pumped central heating system to a
gas fired fully pumped system and am
unsure what arrangement of valves to use.
What are the advantages / disadvantages
of using a 3 port valve instead of two 2 port valves to
control a fully pumped hot water and (single zone )
central heating system?

Go for a 3-way throw over valve with an end switch (3 port) and a quick
recovery cylinder (part L is not quick recovery). The cylinder will take
"all" of the boilers output, reheating in a matter of minutes, and be
cheaper to run. The system will be a "priority" system. These valves are
generally to order, but come fast. A few have the end-switch, like Drayton
and others. The end switch makes it easy to wire up.

The now common 3-port mid-position valve can be temperamental. If going
this route, which I suggest you do not. Use two 2-port valves, unless space
is a problem.

A quick recovery cylinder can be downsized. So a normal 114 litre cylinder
can 80 litres. The 80 litre Telford Typhoon from Travis Perkins is approx
£100. Albion and Range do them too

http://www.albion-online.co.uk

 

[EMC]

IMM,

Thanks for the information. By throw-over valve, do you mean a diverter
valve? I assume that by using this arrangement all hot water from the
boiler will be diverted to the cylinder when demanded. If several baths,
washing machine and shower are used in succession (probably unlikely I
know), would that mean the radiators may not be supplied for some time?

On the subject of quick recovery cylinders, what is Part L? I am also
considering an unvented cylinder and a sealed system boiler. Which unvented
cylinders would you recommend as quick recovery?

Eric

 

[EMC]

Thanks Bill, I'm coming to the same conclusion as the lack of reliability of
the 3 port valves seems to be a widespread opinion.

Eric

 

[IMM]

Thanks Bill, I'm coming to the same conclusion as the lack of reliability of
the 3 port valves seems to be a widespread opinion.

You mean a 3-port mid-position valve. A 3-port diverter is the most
reliable option. One reliable simple head. With two valves you double the
problem. Diverters and 2 -ports tend to use the same heads.

 

[IMM]

Yes, that is the correct terminology.


Yes, but in reality the cylinder is re-heated pronto. The cylinder will be
well re-heated and well into CH mode by the time another bath is run. A
largish boiler may be re-heating the cylinder faster than what the shower
can draw-off the hot water.

As you are buying a new boiler, look at getting a combi to supply the
showers only. Then no expensive, noisy, vibrating, troublesome power shower
pumps. Have the CH section as a conventional system with a 3-way diverter
valve. As the combi's water section will only be used for showers, once or
twice a day, they last quite a time. All the water system, except the
showers will be at low pressure and high flow.

If you are replacing the cold water tank think about a "combi cylinder".
Have a 50-50 split of hot water and cold water storage. Have the cold water
section 115 litres and take all the cold supplies off the cold water
section. This way using a combi boiler for the shower side you eliminate
the cold water tank in the loft, or put the combi cylinder in the loft (well
insulated of course) and have a larger airing cupboard. Telford do the
Trident, which has a 115litre/115litre split. have a look at their web
site. Combi cylinders are simpler and quicker to install.
http://www.telford-group.com/trident.htm Some cylinder makers will provide
combi cylinders to order, in that if you wanted a 115 litre hot section and
115 litre cold section and appropriate tappings, etc, they will provide it.

So you would have:

1. A combi boiler supplying any high pressure showers.
2. A combi cylinder with a large cold water section. providing low pressur
hot and cold water.
3. A DHW priority system.



In April part L of the building regs came into being. It implemented energy
regs to water and heating systems. Part L cylinders means that all cylinder
must take no more than 30 minutes to heat up. This obviously is depending
on the boiler temp being on max, which it should be, and the flow through
the coil. Quick recovery are far superior to Part L cylinder. So, in a
plumbing shop the man may say these are all quick re-heat because they all
conform to Part L. I have heard that being said by counter men.


An unvented cylinder needs to be fitted by a BBA approved fitter. They are
not DIYable. Consider the suggestion I made above, which is cheap and easy
and give lots of flow and high pressure showers. Otherwise fit a heat bank,
rather than an unvented cylinder which requires large bore blow-off pipes to
outside, tundishes, etc. Some heat banks don't even require overflows.

A sealed system boiler is fine. But many combi's are cheaper and you get the
high pressure DHW section for showers for free and a very high output that
modulates. Many wise installers buy cheap combi's and ignore the DHW
section, just connecting it to the mains and capping the hot water draw-off
pipe off.

When fitting a new boiler to an existing system always insert a strainer on
the return next to the boiler to catch ant crud floating around. In fact
some Alpha combi's have a cyclone in the return pipe inside the boiler to
catch the debris.

Heat banks:
http://www.heatweb.com
Also from Range cylinders under "thermal storage" on their web site. Albion
don't do heat banks.

 

[Ed Sirett]

I am just about to embark on upgrading my old oil fired gravity hot water /
pumped central heating system to a gas fired fully pumped system and am
unsure what arrangement of valves to use. What are the advantages /
disadvantages of using a 3 port valve instead of two 2 port valves to
control a fully pumped hot water and (single zone ) central heating system?

IMHO using 2 (or more) 2 port valves is better in every respect than a 3
port valve except that the 3 port (either mid-position or diverter
variants) is marginally lighter on material costs.

If you decide to go the 3 port way - be strongly advised that the
diveter valve variant (either but not both CH and HW) - has been found
wanting by many.

 

[IMM]

If you decide to go the 3 port way - be strongly advised that the
diveter valve variant (either but not both CH and HW) - has been found
wanting by many.

This new to me. A 3 port diverter is as simple as a two port. They use the
same heads.

 

[Andy Hall]

This new to me. A 3 port diverter is as simple as a two port. They use the
same heads.

I had diverter valves of this type in my system from when the house
was built until I ripped it out with the rest of the abortionate
plumbing that they had done in the airing cupboard.

There were four replacements over a 15 year period which I don't think
is impressive. Typically, either the mechanism would stick in the
base or a leak would develop.

Using 2 port versions and having the boiler do the priority control
seems to be a much better solution.


..andy

To email, substitute .nospam with .gl

 

[IMM]

I had diverter valves of this type in my system from when the house
was built until I ripped it out with the rest of the abortionate
plumbing that they had done in the airing cupboard.

There were four replacements over a 15 year period which I don't think
is impressive. Typically, either the mechanism would stick in the
base or a leak would develop.

Sounds like a poor make and compounded by a poorly installed system. They
can be fitted on the cooler return pipe which enhances longevity.

 

[Andy Hall]

Sounds like a poor make and compounded by a poorly installed system. They
can be fitted on the cooler return pipe which enhances longevity.

IIRC, the original was made by Switchmaster? (had a blue motor head),
there were then I think a Danfoss and two Honeywells, with the latter
two lasting about 4 years each. I wouldn't call Danfoss and
Honeywell poor makes as such.

The fitting position was on the return in one of the recommended
positions so no clue there either.

I even went to the trouble of exercising the heating at least weekly
during the summer months so that the valve wouldn't stick. The
failures weren't at any particular time of year.



..andy

To email, substitute .nospam with .gl

 

[IMM]

IIRC, the original was made by Switchmaster? (had a blue motor head),
there were then I think a Danfoss and two Honeywells, with the latter
two lasting about 4 years each. I wouldn't call Danfoss and
Honeywell poor makes as such.

On a far simpler valve you have a failure rate far higher than the more
troublesome mid-position 3 port valve. Sounds like the system was faulty
somewhere.

The fitting position was on the return in one of the recommended
positions so no clue there either.

I even went to the trouble of exercising the heating at least weekly
during the summer months so that the valve wouldn't stick. The
failures weren't at any particular time of year.

Correct and sufficient inhibitor can lubricate valve mechanisms. A two pump
casting Grundfoss Tee setup can be used instead of any 3-port valve,
mid-position or diverter.

 

[Andy Hall]

On a far simpler valve you have a failure rate far higher than the more
troublesome mid-position 3 port valve. Sounds like the system was faulty
somewhere.

There was nothing much else to it so I can't see that that would
influence anything

Correct and sufficient inhibitor can lubricate valve mechanisms.

I did all of that religiously

A two pump
casting Grundfoss Tee setup can be used instead of any 3-port valve,
mid-position or diverter.

Interesting idea and I believe not much different in cost to a
conventional set of pump and valve.




..andy

To email, substitute .nospam with .gl

 

[IMM]

There was nothing much else to it so
I can't see that that would
influence anything

Then you are just unlucky. Can someone be "that" unlucky using three
different makes of valves?

 

[Ed Sirett]

This new to me. A 3 port diverter is as simple as a two port. They use the
same heads.

I don't mean to imply that there was a reliability issue. As you say the
heads are the same as a two port unit. What I mean is that people are
unhappy with a system that cannot simutaneously run the heating and the
water!
More than once I have been asked to 'fix' a system with a diverter valve
that the owners perceived as broken, and as you know, the customer is
always right.

 

[IMM]

I don't mean to imply that there was a reliability issue. As you say the
heads are the same as a two port unit. What I mean is that people are
unhappy with a system that cannot simutaneously run the heating and the
water!
More than once I have been asked to 'fix' a system with a diverter valve
that the owners perceived as broken, and as you know, the customer is
always right.

I assume they have old fashioned British Standard pig of a cylinder and not
a quick recovery. If they had a quick recovery they would not complain as
they would not notice the heating has been off for a few minutes or so.

 

[Ed Sirett]

I assume they have old fashioned British Standard pig of a cylinder and not
a quick recovery. If they had a quick recovery they would not complain as
they would not notice the heating has been off for a few minutes or so.

Whilst a fast recovery cylinder would cetainly have mitigiated the
problem it would (at least for one customer) not have fixed it.
The usage the cusotmer wanted to put the system to was simple: Off for
days at a time then come home and switch both heating and HW on, a
completely reasonable way to operate the system for his lifestyle.
Even a 15 minute delay would really have been unacceptable.