Add-on bypass circuit for combi boiler?

[Al N]

Hi all,

When they installed the standard gas-fired, hot water central heating in my

3-bed semi, the plumbers insisted that my large lounge radiator should not fitted with a TRV, because it needed to be permanently open. I was surprised that the boiler (Ideal Logic 24) doesn't have a built-in bypass, but the installation manual confirms that it doesn't.

My lounge radiator is the biggest radiator in the whole house, since the lounge is the biggest room by far. I rarely use the lounge! I spend most of my time, when at home, either in my small upstairs study or in my smallish bedroom.

I guess I must be wasting a lot of money heating the lounge when heat is not needed there. With my (admittedly scant) knowledge of heating theory, I would have thought it would make sense to have TRVs on ALL the rads, and a bypass curquit added at the boiler, just in case all the TRVs ae closed simultaneously at any point in time. Am I correct?

If so, can anyone recommend a simple/cheap/effective and reliable bypass circuit to add to the above combi?

Many thanks,

A

[Fredxx]

Where's your room-stat?

[Al N]

Fredxx wrote in news:k7rgtf$988$ [e-mail]:

Hi, It's a wireless room stat, which they sited in the lounge.

A

[harry]

There is normally one inside the cabinet. If not, an externally mounted one should be fitted. You are exactly correct.

The reason for fitting one is that the radiator TRVs need a constant pressure to function satisfactorily whereas the boiler needs a constant volume of water to function satisfactorily. The bypass valve allows this to happen.

As the TRVs shut down, the bypass valve opens so relieving the pressure which would otherwise tend to defeat the TRVs.

It also allows the flow of water through the boiler to be undiminished as the TRVs shut down. (There is an optimum water flow through the boiler for efficient running.)

[Fredxx]

The area covered by the room-stat ought to have a radiator without a TRV. The plumber was correct in insisting on this.

The very last thing you want is to have the radiator turned off but the room-stat still requiring heat when all the other rooms are up to temperature.

I take there isn't a hallway or alternative area that can have a room-stat and a radiator without the TRV?

For info, there are a few bypass valves around, an example:

[Al N]

harry wrote in news:683569b4-804e-42f7-a63d- [e-mail]:

Thanks - do you mean I am exactly correct in thinking that I will save money if I put a TRV on the lounge rad (and then add a bypass cirquit)?

Yes, I deduced the above, thanks.

Thanks. That last bit sounds a bit esoteric to my uneducated brain. I think when I installed my own DIY system (in my previous house, in 1997) that there was actual danger of damaging the boiler if you had all TRVs and no bypass, because the pump would be trying to pump the water into a dead end. Luckily, the boiler I used had a built-on bypass, so I had TRVs on all the rads and it worked fine.

A

[newshound]

I have a brand new unused and boxed 22 mm drayton automatic bypass valve from BES, part code 07 02 020, because I didn't realise that the new boiler I put in last year had one built-in. Half price + postage?

[Al N]

Fredxx wrote in news:k7rio0$onc$ [e-mail]:

I could add a very small rad in the very small hall, and have that as the permanently-open rad. But would that be more economical than having a by- pass circuit, and having TRVs on ALL the rads?

Thank you...

A

[Al N]

newshound wrote in news:50a15210$0$33095$c3e8da3 $ [e-mail]:

Possibly. Do you have a valid email addy?

A

[newshound]

Yes; same domain, but stever

[John Rumm]

If you put TRVs on all rads then you risk defeating the boiler interlock effect from the room stat. Currently (assuming the system is well specced and balanced) the lounge will heat up at about the same speed as the rest of the house, and when warm, the stat will switch the boiler off. If you just add a TRV and a bypass, then what may happen is that the room stat is never satisfied and it keeps the heating on all the time.

So moving the room stat, and the uncontrolled rad may make more sense if you can then turn down the temp on the big room.

[John Rumm]

Some boilers have them, some don't.

I don't actually see the logic of harry's comment anyway. Th flow rate of water through the boiler is only part of the dynamic (once you get past the point of "enough" to stop if boiling!), the temperature differential also has a big impact on efficiency - especially with modern boilers. Having a bypass gets round the problem of what happens when the TRVs occlude the flow of water, but does not solve the problem of the "call for heat" demand from the stat keeping it running while the system is not able to accept further heat.

It will work fine like that (from a users point of view), but its fuel inefficient since it keeps the boiler running when the house is already warm enough.

[djc]

As it's wireless remove it from lounge and place it somewhere more sensible, such as te room you are using. Turn off radiator in lounge (fit TRV if you like), turn radiator in room with room stat full on and let the room stat control the temp.

[Al N]

John Rumm wrote in news:wOudnexHYqw [e-mail]:

Thanks for the insight on that. The installer of my present system didn't approve of my idea of having TRVs on all rads and adding a bypass. He commented something about "the boiler would then be firing up all the time". I wasn't sure what he was talking about at the time.

A

[Al N]

djc wrote in news:k7s0im$166$ [e-mail]:

I see that makes sense. Perhaps even better would be to have the rad in the room I use most (my small upstairs study) as the permenantly-open rad, and put a TRV on the lounge rad (and turn it down when heat there is not needed). That would be a safer situation, would it not? (It would eliminate the possibility of someone else closing one of teh TRV's while the lounge rad, as per your suggestion, is turned off.) Agree?

For some reason the installation manual for the boiler names the living room as the place where the permanently-open valve should be. Am I right in presuming that this is merely because they are assuming the living room to be the most-used room?

Thanks.. A

[Al N]

John Rumm wrote in news:iY6dnYqZtc [e-mail]:

Thanks! I could make the rad in my most-used room (study), the uncontrolled rad. Then put the TRV from that rad onto the rad in the lounge. (Lounge rad can then be turned on or off as needed.) Correct?

A

[Fredxx]

I would recommend a hallway or landing. Any habitable room will vary in temperature greatly according to the number of occupants and how it's used. Access to the thermostat is also a consideration.

[Al N]

Fredxx wrote in news:k7s7qe$u85$ [e-mail]:

Yes, I guess that would be ideal. Thanks.. A

[Al N]

djc wrote in news:k7s0im$166$ [e-mail]:

PS. The beauty of this suggestion (from my POV) is that it doesn't involve physically altering the current setup - so the installer's warranty won't become void. So thanks for this idea. It may just be the one I run with - at least until the warranty runs out.

A

[djc]

It is the great benefit of a wireless stat that it can be moved around. So depending on your need you can either: use it to maintain a comfortable temperature in whatever room you are using while using TRVs elsewhere to keep things economically cool or; put it in the coolest room to maintain a overall base temperature, and let TRVs in each room as required.