Valiant ecoTEC plus 837 CH not going past 50

[IggyT]

My HW is fine, nice and hot and steady.
The CH is fine, but the boiler is only heating to 49/50 degrees, which makes the rads only slightly warm.
I have had 3 heating engineers round from British Gas.
New main pcb.
New pump.
Each time they have left and said to my Wife, “it’s fixed”.
When I come home I find it still has the same issue.
So I have done some basic investigations while I wait for yet another engineer.
When I put the boiler into chimney sweep mode, it goes well past 50, boiler is set to 75.
I thought it might be the Hive thermostat they fitted but the thermostat is constantly sending a signal to the pcb when on and switches off when off.
When in chimney sweep mode the rads get nice and hot, so the boiler is capable, but something seems to restrict it.
Any ideas?
Cheers
Iggy

 

[Ricke21]

Have you got trv's on all the rads?? If so remove one where the boiler is or the room with the room stat. If all your rads shut off the waterflow will be reduced making boiler shut off. I've got boiler in bathroom and that rads is always fully open so circulation is free flowing till boild says water is a max temp. Hope that helps

 

[CountryFan]

Could be a fault with the diverter valve. Can't see it being a D code setting as the PCB was changed. Does the temperature shut off at 50?

 

[IggyT]

I've got trv's on all rads bar one.
I will start taking them off.
One thing I have noticed, is a few rads seem to have the flow around the wrong way, e.g., the pipe with the lock shield on the left hand side of the rad is warming up first.
So, in effect, my lock shield is my trv, which is confusing.

 

[IggyT]

The boiler keeps firing lightly at 50 until the thermostat temp is reached, which is never, because the thermostat is at 20 and the house is not getting past 17.8 due to the rads not getting hot enough.

 

[CountryFan]

I've got trv's on all rads bar one.
I will start taking them off.
One thing I have noticed, is a few rads seem to have the flow around the wrong way, e.g., the pipe with the lock shield on the left hand side of the rad is warming up first.
So, in effect, my lock shield is my trv, which is confusing.

If they're bi-directional it won't matter.

 

[IggyT]

I disconnected the hive unit from the boiler.
Put the jumper back in on the 24v RT and put batteries in my old Vaillant wireless controller and bingo, the boiler is now firing nice and strong and reading 68 degrees on the front panel.
So, is there something else you need to do on the hive wiring?

 

[IggyT]

I’ve been experimenting with the Vaillant thermostat and it only makes the boiler go over 50, if I set the temperature to 24 or above (which is the same temp as the hive gives when you press the boost button, except nothing happens with the hive).
Otherwise it just heats at 50.
I was always told that wacking up the thermostat to make the boiler heat faster was rubbish, but maybe not I guess.

 

[CountryFan]

So, is there something else you need to do on the hive wiring?

Not that I’m aware of. Which terminals was it wired to? 24v?

 

[IggyT]

The hive has live-live, neutral-neutral and the control wire to the 230v RT. All on the right hand side of the pcb.

 

[CountryFan]

The hive has live-live, neutral-neutral and the control wire to the 230v RT. All on the right hand side of the pcb.

No reason for it to behave how it has then. I’ve not really encountered this before. I did have it once where I decommissioned an ebus thermostat, wouldn’t go above 50 and carried out a factory reset which got it working. Your new pcb should have sorted that though.

 

[IggyT]

another engineer is due today.
Looking at the last report, the pcb was changed and it made no difference, so the engineer took it back out again.

 

[IggyT]

The engineer has removed the old Vaillant thermostat receiver from the front of the boiler, which seems to have fixed it.
I'm sure I tried that myself and didn't see the boiler go over 50, but maybe I wasn't patient enough.
The rads are nice and hot now and I've got over 18 degrees in the house.
Thanks for all the help, its much appreciated.

 

[CountryFan]

The engineer has removed the old Vaillant thermostat receiver from the front of the boiler, which seems to have fixed it.

Yep, that'll do it because it's a previous Vaillant control