Combi boiler - isolating HW

[Daljit]

Hi

I have a Vaillant Ecotec combi boiler.

My magnetic filter is leaking and I’m waiting on a new seal to arrive in next few days. I’ve removed the filter and switched off valves at the filter pipework and beneath the boiler on the flow and return pipes. I’m hoping to continue using HW as don’t need CH in this weather.

However, I’ve noticed the pressure gauge needle has been creeping up. It was in the red this morning and I opened to flow valve for a few secs to bring it down. This worked but I’m now wondering whether it’s wise to continue using HW with CH isolated.

Also, I was thinking I should run the auto purge cycle in the boiler but again not sure if this should be fine with CH pipes switched off.

Thanks

 

[MeldrewsMate]

You have correctly isolated the boiler, but inadvertently partially opened the re-pressurising system. This is either built-in to the boiler (see the manual) or via an external filling loop.
There should be no problem using the HW function on a combi with the CH isolated, the only difference will be the pump may run-on for longer after a run of hot water usage, trying to remove heat soaked into the main heat exchanger.

 

[Jurassicspark]

the only difference will be the pump may run-on for longer after a run of hot water usage, trying to remove heat soaked into the main heat exchanger.

Why?

How would isolating beneath the boiler cause the pump to run longer, just to remove the heat soaked into the main heat exchanger?

I am not a plumber. I am merely interested.

 

[MeldrewsMate]

Why?

How would isolating beneath the boiler cause the pump to run longer, just to remove the heat soaked into the main heat exchanger?

Because on completing its hot water duty the diverter valve would normally switch to heating mode, sending a small amount of hot primary water out of the flow pipe and receiving cooler water via the return pipe. If it can't send primary hot water that way it will circulate through the hot boiler and lose heat very slowly.

 

[Jurassicspark]

Because on completing its hot water duty the diverter valve would normally switch to heating mode, sending a small amount of hot primary water out of the flow pipe and receiving cooler water via the return pipe. If it can't send primary hot water that way it will circulate through the hot boiler and lose heat very slowly.

Thank you for the reply.

Does this happen with all/majority of the combi boilers?

 

[MeldrewsMate]

Yes.

 

[Daljit]

You have correctly isolated the boiler, but inadvertently partially opened the re-pressurising system. This is either built-in to the boiler (see the manual) or via an external filling loop.
There should be no problem using the HW function on a combi with the CH isolated, the only difference will be the pump may run-on for longer after a run of hot water usage, trying to remove heat soaked into the main heat exchanger.

Hi, removed the loop and there is a v small leak even although the valiant CW valve beneath the boiler is set at closed. Do you know if this be repaired or will it have to replaced?

 

[MeldrewsMate]

Replace it. They're poor quality Geeeerman she-ite.