Vaillant ecoTec Sustain and an Automatic Bypass

[Kncowans]

Hello all

I hope you are well.

This is my first Post here so.....

I recently had a Vaillant ecoTec Sustain (Combi) installed under the ECO Grant Scheme to replace a 14 Year Old Ideal ISAR HE24.

When the Ideal was installed in 2008 for my Mum there was also an Automatic Bypass (ABBV1) fitted.

When I took over the House, I originally had a TRV fitted on all but one Radiator (Hall) which is where the Thermostat is located, however, because of the layout of the House it was nigh on impossible to heat the whole House evenly even after Balancing the System.

Because there was no TRV on the Hall Radiator the Automatic Bypass was fully Closed.

Because of the difficulty in heating the House evenly I installed a Hive TRV on all the Radiators, including the Hall, set the Room Thermostat to Manual and on Frost Protect and then setup each Hive TRV to use Heat on Demand.

Because I now have a Hive TRV on all Radiators the Automatic Bypass was set to Number 2.

Having the system setup like this has worked great and the House heated up evenly,

Since having the new Vaillant ecoTec Sustain installed I have been having some issues.

I have been told that this Boiler has a built in Bypass and that the Automatic Bypass I have is not required, is this correct?

If it is indeed correct that it is not required then should I just close the ABBV1 and let the Boiler handle things?

Worryingly, the Installer, who I had no choice in, did not know what an Automatic Bypass was so asking them would not be useful.

Apologies for the Tome.

Thanks in advance

Kevin

 

[ShaunCorbs]

No the auto bypass in the boiler is just for the boiler as you have smart trvs I would recommend keeping your external bypass in

 

[Kncowans]

Hello Shaun

Thanks for the reply.

Can you give me any tips on how to set the ABBV1 correctly, as it is at the moment, on 2, the Bypass Pipe is very Hot and the Radiators do not give off much Heat.

Thanks in advance

Kevin

 

[John.g]

That setting is way too low, set it to say 0.35 which is 3.5M and see if it cools down, if not increase it a bit further. Ideally, when all the rad trvs are almost fully closed you want the ABV just opening, a bit of trial and error will get you a reasonable setting.

A quick look at the installation manual shows that the internal by pass has two settings, 2.5M and 1.7M, so perhaps just set the ABV to 0.25 initially and then incrementally increase it until it cools down (another indication that its closed fully is maybe all noise ceases).

 

[Kncowans]

Hello

Thanks for the reply.

With the old Boiler, if the Bypass was set to anything above 0.2 the Boiler used to Overheat.

When the new Boiler was installed, the Installers just left the Bypass at the same setting.

With the new Boiler, with the Bypass set at 0.2 I get a lot of noise like bubbles in the Boiler, turning the Bypass up to 0.3 helps somewhat but the Bypass Pipe is still Hot.

Thanks in advance

Kevin

 

[John.g]

There could be a bit of crap under the valve seat keeping it open, it also takes a bit of time for the piping to cool down, just increase it very temporarily to max 0.6? and see if it cools down then gradually decrease it again, don't know why or if the internal by pass is set so low as generally combi boilers will have a fairly high pump pressure for the HW plate exchanger. What make of ABV do you have and is it noisy in operation?.

 

[Kncowans]

Hello

Thanks for the reply.

The Automatic Bypass is the Tower ABBV1 Auto Bypass Valve.

In use, the Bypass is Silent.

The Boiler was installed on January 12 2022 including a Chemical Flush using Fernox F3 and on February 15 I had all new Radiators installed, the old Radiators were 34 Years old, and a PowerFlush (Re-Flush) so there should not be any debris in the system, hopefully.

Thanks in advance

Kevin

 

[John.g]

Shut it off anyway and see if the pipes cool down, if not, replace it with a Honeywell Du144 or the like.

 

[Kncowans]

Hello

Thanks for the reply.

I set the Bypass to 0.35 as you suggested a few Posts back at 08:50 and I just checked the Bypass Pipe and it is definitely cooling down.

Thanks in advance

Kevin

 

[Kncowans]

Hello

I think there has been some progress.

The Heating was on with three Radiators calling for Heat and the Bypass Pipe was cooling down.

After the last Radiator reached its Temperature the TRV closed and the Bypass Pipe got Hot.

This is with the Bypass set at 0.35.

Thanks in advance

Kevin

 

[ShaunCorbs]

With everything open eg all trvs on turn the bypass until it just shuts you might need to do a / move it up a notch at a time until you get no flow through etc

 

[Kncowans]

Hello

When two or more Radiators are calling for Heat then the Bypass Pipe is cool, however, with only one Radiator calling for Heat the Bypass Pipe is Hot.

Does this mean I need to Close the Bypass slightly more?

Thanks in advance

Kevin

 

[ShaunCorbs]

No that’s how it’s supposed to work and is set correctly