Vaillant ecoTec plus 637 Nest controls and pump overrun

22 Feb 2016
Reaction score
United Kingdom

I've had an ecoTec plus 637 in for four years now running two zones and unvented cylinder with the VRC470, VR61 and a VR81. Sadly we just converted the basement and added another zone and Vaillant technical said I couldn't expand my install without moving to their new VRC700 range.

I've fancied getting a Nest for a while so I took the black Friday sales as an opportunity and got three to control all the zones.

I've got it all connected up but noticed the pump overrun making some noise when a zone closed. Previously overrun was handled by the Vaillant controls and we have no auto bypass.

I can add an auto bypass for sure, but I wondered if there is a connection to take off the pump back to one of the zone valves e.g. the ground floor zone, where I could let the pump overrun circulate?

Any thoughts would be appreciated!


Sponsored Links
Sorry this is a bit cut and paste, but I find that there are lots of variants of Vaillant's that are 'the same but different' :confused:, so I always like to check the appropriate manuals.

Adding the Nest shouldn't have made any difference to the pump overrun. With the ecoTec plus 637, the pump is wired directly to, and controlled by the boilers integral circuit board, in just same way as other boiler components such as the burner and the fan. This is because, only the boiler will know how long to run the pump for, once the external controls have stopped calling for heat.


The installation manual for the ecoTec plus 637 says this about it:

Overrun description.JPG

Regarding the bypass, it's built in. Again from the ecoTec plus 637 manual.

by pass.JPG
These do have a built in bypass but if it's noisy you might need an external one to reduce the noise. Need's to be tee'd in on the main flow and return but before any zone valves
Sponsored Links

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local