Vaillant EcoTec Plus 938 temperamental in heating mode

[Deleted member 120897]

One for Shaun John ????

Yep or Dan/Lou?

 

[John.g]

Pump was always at 100%. Will post some charts on temps later

It's still a strange one though because if the diverter valve was working originally its hard to understand why not enough water flowed even if the bypass was fully closed, the diverter valve should have directed the primary water to the zone(s) valves which presumably opened at the same time and even one rad/towelrad should provide the minimum flow necessary.

 

[John.g]

Yep or Dan/Lou?

I actuall registerd under a new name and Lou welcomed me on board so I replied explaining my problem.

 

[Dan]

Why do I have to reset my password each time I log out since this morning?.

Hi John,

We're toying around with a new advertising partner and that might have something to do with it.

Although it does appear as though your computer isn't remembering your logins, and you're simply resetting your password to login, rather than using the last password you chose?

(Don't ever write passwords in here, I'm sure you wouldn't have done already but I thought I'd let you know and say this)

If it happens again could you please try to clear the browser cookies, close the browser down, then reopen it, login, and check the box to remember you each time you visit (only providing you're using a computer only you have access to.

 

[John.g]

Hi John,

We're toying around with a new advertising partner and that might have something to do with it.

Although it does appear as though your computer isn't remembering your logins, and you're simply resetting your password to login, rather than using the last password you chose?

(Don't ever write passwords in here, I'm sure you wouldn't have done already but I thought I'd let you know and say this)

If it happens again could you please try to clear the browser cookies, close the browser down, then reopen it, login, and check the box to remember you each time you visit (only providing you're using a computer only you have access to.

Thanks Dan, Yes, I'm using my saved password each time in resetting and clicking the remember me box and also the stay logged in box.

 

[skvortsov]

It's still a strange one though because if the diverter valve was working originally its hard to understand why not enough water flowed even if the bypass was fully closed, the diverter valve should have directed the primary water to the zone(s) valves which presumably opened at the same time and even one rad/towelrad should provide the minimum flow necessary.

Well, I think I spoke too soon. It's doing the same thing again... Adding more turns on the internal bypass did not help - put it back to the original position now. Does this boiler not have a flow rate sensor for the heating circuit? I'm sure the flow rate is good, because I have 3 towel rails all fully open and they heat up very quickly when the boiler outputs 60C.

So the situation now is that it would sit at minimum flame for a while with return temperature about 38 and flow about 42... If I turn the hot water it heats it up perfectly fine - flow goes above 60 immediately... Then after DHW pump overrun it goes back to heating mode and temperature drop to 40 again. What else could be wrong?

 

[John.g]

In heating mode your boiler has a minimum output of 6kw so assuming that this is correct then a deltaT of 4C (flow/return) = a flowrate of > 20 LPM so no problem there it would seem.

Not sure what you mean by DHW pump overrun, if its a combi?? then the primary circ pump (the only one?)
may go in to overrun when finished with DHW and depending on the pump overrun time could reduce the temperature from 60C to 40C but should then fire up on CH/UFH and very quickly go to 60c again. Are you sure that there is nothing (remotely) setting the boiler flow temp to a very low value when CH/UFH requested?.

 

[skvortsov]

DHW pump overrun is what it shows in the Status menu after I turn the hot water off. After it's done with overrun and back to heating mode - flow temperature doesn't want to go to 60 and stays about 40.
Both zone vales are just simple 240V, no fancy smart controls connected to the boiler itself. So I'm pretty sure there is nothing setting Flow temp to low value

 

[skvortsov]

Just used your formula to calculate the flow rate assuming it is firing at min 6kW. If I have 4 degrees flow/return difference it gives me 21.5 l/min. Is this reasonable flow for 3 towel rails?

 

[John.g]

Yes, probably, especially with the pump on 100% output. I can't see you having a flow problem.