Vaillant ecoTec plus 418 cycling

[dave654321]

Hi, I have just had a Vaillant 418 ecotech plus installed, a new castle grade 3 cylinder, variable speed interpart pump and new 3 port interpart valve. External controls are Salus IT500.

When on water only the boiler is cycling. Top water dial is set to full, but I understand this doesn't do anything without external weather controls fitted. Bottom dial is set to 69 degrees.

When heating is running the cycling doesn't occur. The boiler can get to S.30 - "No heating demand from external controls".

From what I've read it's to do with the temperature of return too close to that of flow and the heat loss in the radiators drops the return temperature sufficiently. I did see S.53 - "appliance is in within the waiting period of the operation block function due to water shortage (VL-RL spread too big)." The installer adjusted the gate valve between the flow and return pipes near the cyclinder. The pipework is per the install diagram except the gate valve is in place of the automatic bypass. I'm told correctly adjusted this is the same function.

The house is 5 bed detached with 11 radiators.

This appears to be a common problem. Any help is much appreciated.

 

[ShaunCorbs]

if its only just been installed get the heating engineer back

 

[lame plumber]

to rewire the 3 port

 

[Chalked]

Very simple electrical fix.
Get the sparky to read the installation instructions.

 

[dave654321]

Thank you for the replies. Coming back at the weekend. I would still like to understand more about it if possible.
The 3 port valve appears to work correctly in that it directs water to cylinder, rads or both as selected by the salus controls.
Is the rewiring to allow the valve to direct the flow to the rads to lose enough heat so the boiler return has cooled enough to give the correct flow / return differential when just hot water is selected.
When the rads are on this doesn't happen. I guess due to the temperature drop across them and the larger loop.
I read that the pump speed should be 3. It's an automatic pump and had selected 12 rpm. Setting to 3 runs it at 32rpm. Is that true.

Apologies it's only 4 bed house. Wishful thinking 😉

Best regards
Dave

 

[gassafe]

Sounds like flow water going straight back into return through that gate valve... Most 3 port systems don't require a bypass & a gate valve does not do the same job! I would say shut the gate valve

 

[dave654321]

Turning the interpart pump to 3 from auto seems to have done the job. Boiler now gets to S.0 (no heat demand) and S.30 (No heat demand: controller).
Is it ok to run the interpart pump at 3 without risk of damaging the boiler / internal pump?
Not able to adjust the gate valve yet as don't have a key that fits. I guess a combination of external pump speed and bypass flow shut off could be the answer. Guessing after closing the valve the pump could run slower unless 3 is the right setting for this boiler?

 

[solutions]

I am sure regardless of weather comp the boiler can be wired to identify between a demand on rads and a demand on hot water. You should be able to specify different flow temperatures on the boiler.

 

[kris]

Just remember a gate valve is different to an automatic bypass because a gate valve when opened however slightly opened is open .... an automatic bypass when set opens when a certain pressure is put apon it . The gate valve will always allow a degree of water past it depending on how open it is but if it's hardly open and every rad is shut then it puts more pressure on the pump as restrics the flow.