Vaillant Ecotec Plus - DHW Temp Low

[niallac]

Hello all,

I have a 15 month old Vaillant Ecotec Plus, installed by a trusted plumber, who has done a star job for us for 15 years. When installed, he flushed the CH system (which was spotless anyway, we have fairly soft water) and installed a quality filter. It's been serviced regularly and fine until about 6 months ago.

At that point, it started making a sort of machine-gun type rattle when the CH pump was running, and the DHW Temp wouldn't get above 57C, despite the stat being set to 65C. Plumber said call Vaillant, Vaillant engineer attended, and changed the main gas valve and flow meter due to sulphate contamination (excuse the terminology, I'm non-industry) and it was fine until now.

On Friday night, we had the mother in-law round to babysit, so ran the CH hard for the first time in a while (she's 85 so likes it warm). I noticed the machine-gun noise again at that point, although it had continued after the engineer visit when ever the CH got hot. CH loop pressure is normal, even when hot.

Today, the DHW Temp dropped off again - refused to go above 57C, and the bath filler was lukewarm. It's about 16C outside here just now (roasting for Edinburgh) and back in March I was blaming the low temp of the incoming main supply.

I turned the boiler electric supply off at the mains then back on 10 min later, and the DHW Temp was back to normal.

'Live Monitor' shows nothing unusual.

Any ideas? I can get Vaillant back out on warranty, but I'd like some choice questions to ask this time.

Thanks in advance.

Niall

 

[DP]

A combi will elevate cold water by 35 degree C
At full flow doubt you will get 57 degree at the tap

 

[niallac]

A combi will elevate cold water by 35 degree C
At full flow doubt you will get 57 degree at the tap

Hi there, DHW temp quoted is as displayed on the boiler, not measured at the tap. As per my original post, it goes back up to the preset level following a restart of the boiler.

 

[DP]

57 degrees, if selected on boiler control is the target temperature

What it means is that hot water will not exceed 57 degrees, does not mean it will get to 57. It may get to 57 and be controlled at that temperature if the tap flow is reduced

To achieve 35 degree temperature rise, gas pipe needs to be correctly sized ( or not restricted) to feed the boiler with required amount of gas, heat exchanger and burners need to be clean and combustion be at correct setting, flow rate at the tap needs to be as specified for that model and finally the diverter needs to divert primary flow correctly

If hw control moved, temperature display also should change indicating that component works

 

[undertrained]

Have had noises from diverter valve before now, so this could be your issue.

 

[niallac]

In case this info helps anyone else, Vaillant reattended and were unable to identify the fault. I explained the symptoms to the tech though, and he replaced the diverter valve anyway.

Now sorted, DHW is scalding, no funny noises.

Thanks again for the help.