2 x 2-port versus 1 x 3-port diverter valve

hfr254 · 14 Jul 2009

All pumped central heating system using 2 2-port valves to control Heating & DHW. Replacing boiler, pump and controls soon what are the merits of 2 x 2-port valves versus 1 x 3-port diverter valve.

If I stay with 2 x 2-port valves and have TRV's on ALL rads do I still need a small bore bypass around the boiler to help it dump the remaining heat when the 2 x 2-ports close.

simond · 14 Jul 2009

What output is the new boiler and what make and model?

Without this basic info it is impossible to answer.

hfr254 · 14 Jul 2009

The replacement system is not yet in place, but going for a Glow Worm conventional condensing boiler 30 HXI non combi

leakydave · 14 Jul 2009

Well for one thing you could have an upstairs heating circuit and downstairs heating circuit... might save a bit of fuel over the years, especially in a larger house... so three 2-port valves: 2 heating 1 water. If a small house 3-port valve probably easier.

S plan will need auto bypass as all valves could close and pump over run kick in.

Razor900 · 14 Jul 2009

If the house is big enough to need a 30kw boiler it's going to need an s-plan with 28mm primaries, what size is the property?

D_Hailsham · 14 Jul 2009

hfr254 said:
The replacement system is not yet in place, but going for a Glow Worm conventional condensing boiler 30 HXI non combi

Why such a large boiler? I could understand the need for a 30kW if you were installing a combi, but 30kW for heating suggest that either you have a very very large house, or the person who recommended it does not know what they are talking about.

Use the EST online boiler calculator to find out what size boiler you need.

Biggles.. · 14 Jul 2009

Or it could be that its sized for a large dhw reheat requirement.

D_Hailsham · 14 Jul 2009

lcgs said:
Or it could be that its sized for a large dhw reheat requirement.

If you only need to allow 2kW on top of the heating requirement for a 'normal' house, how big will the house have to be to need 15-20kW extra?

Deleted member 105431 · 14 Jul 2009

D_Hailsham said:
lcgs said:

Or it could be that its sized for a large dhw reheat requirement.

Click to expand...

If you only need to allow 2kW on top of the heating requirement for a 'normal' house, how big will the house have to be to need 15-20kW extra?

some good quality high recovery cylinders have 15kw coils on a 170 L cyl, they reheat in under 10 minutes.

Razor900 · 14 Jul 2009

And there are some like the geminis that have much higher rated coils but no one would put an u/v on a y plan unless it was already there, especially at those inputs.

We will have to wait and see how big his house is!

Biggles.. · 14 Jul 2009

D_Hailsham said:
lcgs said:

Or it could be that its sized for a large dhw reheat requirement.

Click to expand...

If you only need to allow 2kW on top of the heating requirement for a 'normal' house, how big will the house have to be to need 15-20kW extra?

Typical misunderstanding of cylinder heat loss and the rubbish Part L course quoting 2-3kw for cylinders.

alot of cylinders have high recovery coils of 20kw and its not that uncommon to deplete a high content cylinder after 2 or 3 baths or good long showers.

You want maximum reheat and,in systems without hot water priority you might even have heating at the same time.Saying to customers set your hot water times different to your heating just so you can undersize your boiler is a poor effort.

Size for worst case maximum demand.

Personally not installed a y plan in years

stem · 15 Jul 2009

My new boiler needed a bypass, so I had the same dilema and decided to stick with the "S" plan and add a bypass. Several reasons for this.

1). When the radiators are in use and the room thermostat switches off, a 3 port valves spring returns it to the hot water only position so the pump overrun circulates the hot water from the boiler through the cylinder, each time this happens the temperature of the stored water in the cylinder rises slightly, if the themostat switches on and off quite frequently this "unwanted" temperature rise could be significant.

2). Under a certain combination of operating circumstances it is possible for a three port valve motor to remain energised even when everything is off. This wastes electricity and shortens the life of the valve motor.

3) An automatic bypass can maintain the boilers recomended flow rate when many TRV's are closed or part closed. I suspect this may also make the pumps life a little easier and extend it's life.

seco services · 15 Jul 2009

stem said:
1). When the radiators are in use and the room thermostat switches off, a 3 port valves spring returns it to the hot water only position

no it don't the grey wire from the hw off or satisfied will hold the valve in its last position.
so if heating last port of call the valve will be held heating open hw closed.

it will only return to hw open is hw is still calling for heat.

Agile · 15 Jul 2009

hfr254 said:
If I stay with 2 x 2-port valves and have TRV's on ALL rads do I still need a small bore bypass around the boiler to help it dump the remaining heat when the 2 x 2-ports close.

You certainly do not need that as its not recommended or approved! The correct solution is to fit an automatic bypass.

Like everyone else I expect your boiler is seriously oversized. That will reduce the operating efficiency and is contrary to the energy saving advice on boiler sizing.

Most houses need 12-18 kW !

Tony

stem · 16 Jul 2009

seco services said:
stem said:

1). When the radiators are in use and the room thermostat switches off, a 3 port valves spring returns it to the hot water only position

Click to expand...

no it don't the grey wire from the hw off or satisfied will hold the valve in its last position.
so if heating last port of call the valve will be held heating open hw closed.

it will only return to hw open is hw is still calling for heat.

Of course you are correct!

I Don't know what I was thinking of. I even contradicted myself because in my second statement I referred to the valve remaining energised.....time to go and lie down in a darkened room I think.

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2 x 2-port versus 1 x 3-port diverter valve

Deleted member 105431

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