Automatic bypass valve versus open radiator

[colin_]

Hi

I have an Evohome which maintains the set temperature and so when it powers the boiler most of the radiator valves are closed with one or two slightly open, basically just "topping up" rather than heating fully.

This means that the automatic bypass valve (ABV) has to open as well.

Now, rather than use the ABV I could leave say the bathroom radiator fully open instead.

I would appreciate it if someone could let me know the pros and cons of each approach and what is best practice.

My (probably incorrect) ramblings so far are

If ABV used then, whilst most radiator valves closed and a couple very slightly open, water is flowing and it is returning the water back to the boiler at much the same temperature as it left (as basically just 50m of copper pipe run) and so the boiler may modulate down. This means that the radiators that do require heating may not get it and if they do then potentially at a lower temperature. Also those further on from where the ABV is fitted may miss out as the water is diverted?

If ABV is not used then the bathroom radiator will be taking heat even when not required such as when the hot water cylinder is heating or there has been a large step jump in desired temperature such as in the morning.

Thanks
Colin

 

[gmartine]

That is the problem when hyper controls are put on every emitter and you're not doing the boiler much good either unless it has a very high modulation rate. Open up bathroom, hallway and perhaps one other room so it has something to do.

 

[colin_]

That is the problem when hyper controls are put on every emitter and you're not doing the boiler much good either unless it has a very high modulation rate. Open up bathroom, hallway and perhaps one other room so it has something to do.

The boiler can modulate down to 10% (so 3kW) and the bathroom radiator is approx 1Kw.

Would that be sufficient (to maintain the boiler min flow rate requirement) and is it preferable to the automatic bypass valve?

Thanks
Colin

 

[John.g]

IMO the biggest and really the only problem with using ABVs is that the modern smart pumps simply do not provide true constant curve control, they act, in part, at constant pressure, right where you need constant curve control for correct ABV operation. The only one I've seen that did is a DAB Evosta 4-7M pump (no longer made).
Nobody seems to know why this is so.

 

[oz-plumber]

It would be far better to have uncontrolled radiators to by-pass the minimum requirements of the boiler than use the boilers ABV.

The additional heat won't kill you and may be beneficial.

What will almost kill you would be replacing boiler parts that have failed due to having the boiler trying to operate below it's minimum operating output.

Try to make your system as efficient as possible - within the minimum parameters of the boiler installed.

Your boiler and your wallet will appreciate will appreciate it

 

[colin_]

It would be far better to have uncontrolled radiators to by-pass the minimum requirements of the boiler than use the boilers ABV.

The additional heat won't kill you and may be beneficial.

What will almost kill you would be replacing boiler parts that have failed due to having the boiler trying to operate below it's minimum operating output.

Try to make your system as efficient as possible - within the minimum parameters of the boiler installed.

Your boiler and your wallet will appreciate will appreciate it

Thanks for the reply.

The ABV is external to the boiler (the Worcester does not have one) and is a run of ~ 50m round trip.

The Worcester is 30kwh and can modulate down to 10%.

I presume just one radiator fully open will suffice (as if too many or in summer it may use more gas in heating it up when just the water cylinder is required)?

Regards
Colin