do I need install an additional Auto bypass valve if the combi already has one?

So, the heating system that I inherited with this flat has a Volkera Sabre he 25 plus combi boiler and 8 rads, each with a trv.

None of the trv valves have caps on, so they have been fully open since the day I moved in.

I'm wanting to fit a few new rads as the current ones are too small for the respective room size and whilst I was at it, was intending to fit new trv's.

I know that if you have system with all the rads having a trv, then I would need an Automatic bypass valve.

Looking through the manual, (http://www.upperplumbers.co.uk/PDF/Manuals/Boilers/Sabre_HE_Combi_install.pdf
it says

3.6.2 AUTOMATIC BY-PASS The appliance has a built-in automatic by-pass. However it may be necessary to fit an external bypass should the design of the heating system require such. In any case, the design of the system should be such that it prevents boiler ‘cycling’.

So I'm left wondering if I need one.

And supposing I do, how do know the level to set it at?

In terms of where to position it.

IMG_2972_adjusted

• james19000
• 4 Sep 2020

IMG_2967_adjusted

• james19000
• 4 Sep 2020

Screen Shot 2020-09-04 At 21.59.58

• james19000
• 4 Sep 2020

Thanks for reading and advise.

james19000 said:

I know that if you have system with all the rads having a trv, then I would need an Automatic bypass valve.

Click to expand...

I can only think of a couple of boiler models ever that allowed TRVs to be fitted to every rad...and the boiler incorporated a flow sensor to comply with building regs.

TRVs must not be fitted to all rads.

Normally a room thermostat is fitted to a hallway or living room and the radiator in that zone is fited with 2 lockshield valves (ie. valves that are not user adjustable and have plain caps). This is for compliance with building regs.

So in answer to your question it is not normally necessary to have an additional bypass valve as there will always be flow through the lockshielded rad and even if that's not quite sufficient the boilers integral bypass ensures adequate flow through the heat exchanger.

Thanks Gasguru.

I've read that as well. which means who ever did the installation here didn't follow convention.

I've also been reading up on putting in a thermostat and bypassing the internal clock on the combi.

https://www.diynot.com/diy/threads/hive-install-gone-sideways-advice-needed.488863/

though having read the following post, it doesn't fill me with confidence.

fit TRVs to all rads except one, and install a room thermostat in the room with the rad without a TRV , you have to do this in England and Wales to comply with relevent regs

ianmcd said:

fit TRVs to all rads except one, and install a room thermostat in the room with the rad without a TRV , you have to do this in England and Wales to comply with relevent regs

Click to expand...

thanks, i'll do that.

Any recommendations as to thermostat.
I was thinking of getting a nest.

additionally I was thinking of putting the thermostat in the main hall.

thank you

yes nest is fine,but you cant use two thermostats, just fit the nest where the rad without a TRV is