Combi Boiler - bypass radiator necessary?

[jhs14]

Hi all,

I've recently installed a smart heating system (Evohome) which uses TRVs to control each radiator independently. I've put an Evohome TRV on all the radiators, including the bathroom radiator which was previously fitted without a TRV to act as a bypass radiator.

The idea is that Evohome tells the boiler to fire whenever more than one TRV calls for heat, and turns the boiler off when none of the TRVs call for heat. Therefore in theory, there should be no need for a bypass rad.

I've noticed however that when the last TRV switches off, there is a short delay before the boiler itself turns off. In that time, as soon as the last TRV closes, the boiler starts making a load groaning noise - I can't work out where from exactly but it doesn't sound too happy. I'm assuming it's the pump making this noise, caused by the hot water having nowhere to go.

I was under the impression that a modern combi boiler (Glowworm Ultimate) would have an automatic bypass fitted, and therefore there would be no need for a dedicated bypass radiator?

I could solve the problem by reverting the bathroom radiator back to being permanently on, but I'd rather not if possible.

Thanks,

 

[Madrab]

Depends on whether the boiler has an internal bypass or not. Most Ultimates don't have an internal bypass and ideally you need an automatic bypass (ABV), unless it's on a Y Plan.

The bypass is to facilitate flow through the boiler to dissipate heat and avoid the pump overrun pushing against a closed circuit when the TRV's/Zone valve's shut down, that will be where your noise is coming from. You need to correct this quickly to avoid damage to your pump and boiler.

Reinstate your bathroom rad as a manual bypass just now and look to getting an ABV fitted.

 

[simond]

You have to have an auto bypass with Evohome or the boiler will overheat. Some boilers such as Vaillant ecoTEC 6, 8 and 9 series provide one, most do not.

 

[Dan Robinson]

Can't beat a bit of RTFM sometimes .

 

[dilalio]

http://www.googlebattle.com/index.p...mption+is+the+mother+of+all+****ups&submit=Go!

 

[Madrab]

Can't beat a bit of RTFM sometimes .

 

[jhs14]

Thanks for the replies all.

Can't beat a bit of RTFM sometimes .

I had RTFM - the boiler manual states that there is an internal non-adjustable bypass. The boiler isn't cutting out, just sounding unhappy, so maybe it just needs a more sensitive bypass. I'll fit an external ABV and see if that cures it - for now the bathroom rad is acting as the bypass.

 

[Madrab]

What model of ultimate is it? Yeah, it won't be happy as the heat can't go anywhere and the pump cavitate's on overrun, pushing against the closed system.

Going back to the bathroom rad fully open should have quietened the boiler back down? An ABV will allow you to go back to fully controlled by the EVO, just make sure it's set up correctly.

 

[jhs14]

What model of ultimate is it? Yeah, it won't be happy as the heat can't go anywhere and the pump cavitate's on overrun, pushing against the closed system.

It's an Ultimate 30c. Unless I've misunderstood the manual and diagram, there is an internal non-adjustable automatic bypass fitted. Clearly not sufficient though.

Going back to the bathroom rad fully open should have quietened the boiler back down? An ABV will allow you to go back to fully controlled by the EVO, just make sure it's set up correctly.

Yes - the bathroom is within earshot of the boiler, and when all other rads are already closed, you can hear the boiler groaning the second the bathroom TRV closes. With the bathroom rad open all is quiet again.

 

[Agile]

The internal bypass is solely to protect the boiler and give just enough flow to ensure the over heat devices will operate.

Tony

 

[DP]

It's an Ultimate 30c. Unless I've misunderstood the manual and diagram, there is an internal non-adjustable automatic bypass fitted. Clearly not sufficient though.

Is this boiler not heat only with pump fitted externally? If so, how does the internal bypass ( do not remember seeing one last time I looked at an ultimate) function with pump fitted externally?

 

[Dan Robinson]

Glowworm have recycled the name I think.