Potterton Netaheat 16/22 - Pump constantly running?

[Johny2b]

Boiler: Potterton Neatheat 16/22 Programmer Potterton EP3000

The boiler is functioning correctly, however I noticed the pump runs continuously. I checked the motorised valves microswitches which are operating fine. Next I replaced the boiler thermostat (which has built in pump over run stat), but this did not solve the problem.
This to me suggested either the programmer or the pcb? I removed the programmer (its one of those that sits on a back plate so easy to do) and the pump still continues to run constantly.
So could this be the PCB? Its an 407676, which I don't mind changing but is there any way of probing this out with a meter to prove the problem? Or any components on the pcb that could possibly cause this issue? Since other than this, the boiler if functioning correctly.

I am regularly now turning off the boiler at the mains, since I want to make sure the pump does not burn out ... Do you think this is necessary or Iam i being overcautious?

Any help much appreciated...

 

[corgiman]

Do you have a three port valve or two two port valves??

 

[gas4you]

The last netaheats I repaired only had a 2 wire boiler stat

Agree with corgi go back to checking the zone valves. This is a rather basic boiler for things to go wrong on.

 

[corgiman]

The last netaheats I repaired only had a 2 wire boiler stat

Agree with corgi go back to checking the zone valves. This is a rather basic boiler for things to go wrong on.

Thats what I was thinking dave

they dont have a pump over run I am sure

 

[Johny2b]

Two two port motorised valves....
It does have a pump over run stat, I am sure of it but it was only fitted on the 16/22 model and forms part of the boiler stat. I checked both of the motorised valve microswitch's which are open circuit when not engaged, and closed circuit when engaged.. as it should be.. Anything else I should check on them?

You can see the specific install instructions here...

http://www.partsarena.com/baxi
by following...
Catalog » Potterton » Boiler » Netaheat » 16/22E (GC No. 4160166) » Installation Instructions » Netaheat Electronic 6/10, 10/16, 16/22

 

[Agile]

This one does not have pump over run but the Potterton Netaheat Profile does!

They should not reuse names in a way that can be confusing!

Tony

 

[corgiman]

not according to the thing that you pointed us to

the boiler stat is just a cut of switch (phial and bellows obviously) look at the picture of the boiler stat it only has two connections

also I am sure that the pump is not wired to the boiler so there is no way the boiler can control the pump

Sorry but I am two fat and lazy to go to me van to check me wiring bible to verify this.

Does the boiler fire up at odd times as well as the pump running all the time?

 

[Gasguru]

Two two port motorised valves....

Some versions of the old MK IIF had pump overrun.

With 2 x 2 ports check you have a bypass valve fitted and that it is open sufficent to allow flow with the zone valves closed.

 

[Johny2b]

Guys, thanks for your comments. I thought I directed you to the correct boiler diagram, but just in case click on this image below. As you can see on the 16/22 it has dotted lines showing the additional components with three additional wires for the pump overun stat.



Thing is I have already changed the boiler thermostat (which includes the pump ver run stat in one piece), and its not solved the problem.
Looking at the wiring diagram it looks like the overheat thermostat takes a connection from the pcb and feeds the pump overun.

Would someone be so kind as to describe the sequence of events logically when this boiler operates... Eg

What I (think?) happens is the timer/room stat/etc feed power to the one of the motorised valves when water/heating is required. This opens the valve and engages the valve microswitch, which in turn provides power to the pump.

The pressure switch (?) notifies the control unit (pcb) which in turn manages the gas control valve & fan, etc.

I assume the overheat stat & pump over run ensures if the boiler is overheating it contiunes to run the pump to extract any hot water until it cool sufficiently?

sorry guys iif I have this all wrong, would welcome correction as required.

In answer to this question "With 2 x 2 ports check you have a bypass valve fitted and that it is open sufficent to allow flow with the zone valves closed." Yes there is, and it's fully open. I assume this is to ensure the boiler has a circuit to pump water if the overheat stat is running the pump?

Thanks guys

 

[gas4you]

Yet again something else learn't. Never seen one fitted though

 

[Agile]

In answer to this question "With 2 x 2 ports check you have a bypass valve fitted and that it is open sufficent to allow flow with the zone valves closed." Yes there is, and it's fully open. I assume this is to ensure the boiler has a circuit to pump water if the overheat stat is running the pump?
Thanks guys

That sounds as if you dont have a proper auto bypass valve!

If its a gate valve and fully open it will be shorting out the heating circuit and possibly even encouraging the boiler to overheat. Its a common self inflicted boiler fault.

It should be closed and then with pipes cold and boiler started up opened just enough for a small flow to show up by heating the return side. At this setting tighten the gland nut and remove the wheel head.

Tony

 

[Johny2b]

In answer to this question "With 2 x 2 ports check you have a bypass valve fitted and that it is open sufficent to allow flow with the zone valves closed." Yes there is, and it's fully open. I assume this is to ensure the boiler has a circuit to pump water if the overheat stat is running the pump?
Thanks guys

That sounds as if you dont have a proper auto bypass valve!

If its a gate valve and fully open it will be shorting out the heating circuit and possibly even encouraging the boiler to overheat. Its a common self inflicted boiler fault.

It should be closed and then with pipes cold and boiler started up opened just enough for a small flow to show up by heating the return side. At this setting tighten the gland nut and remove the wheel head.

Tony

Sorry I may have misled. I checked this in the dark and did not look properly.

Within the hotwater tank, the 22mm hw pipe has a T which route to each motorised valve. There is also a 15mm pipe before off this T which I can only assume is the bypass but I cannot see any auto valve installed (this could be under the floor or behind the boiler) (cab post a picture if helpful)

What I dont understand is how this would affect the pump running continually? Cheers

 

[Johny2b]

Agile you were 100% on the button. Instead of an automatic bypass value it had an isolating valve that was left completely open - therefore allowing the bypass circuit to remain at the high temp therefore not providing a route for the boiler to cool down.
I have replaced this with an auto bypass valve (Honeywell DU144), the only question remains is what's the best setting....
The instructions suggest that you need the pumps curves (Grundfos Selectric UPS 15-50) (http://net.grundfos.com/Appl/WebCAP...code=S100FAM&appcode=&pdfid=1229&language=ENU)
and the boiler min flow rate. The only thing is I cannot find the boiler min flow rate in the install manual.

Can I set this up a different way... eg Let everything cool down, turn on heating - adjust the bypass valve until hot water just starts to pass through - then back it up a little? Is this good enough an approach?

Guys thanks so much for help so far...

In answer to this question "With 2 x 2 ports check you have a bypass valve fitted and that it is open sufficent to allow flow with the zone valves closed." Yes there is, and it's fully open. I assume this is to ensure the boiler has a circuit to pump water if the overheat stat is running the pump?
Thanks guys

That sounds as if you dont have a proper auto bypass valve!

If its a gate valve and fully open it will be shorting out the heating circuit and possibly even encouraging the boiler to overheat. Its a common self inflicted boiler fault.

It should be closed and then with pipes cold and boiler started up opened just enough for a small flow to show up by heating the return side. At this setting tighten the gland nut and remove the wheel head.

Tony

 

[namsag]

Your original fault of pump running constantly is not going to be cured by doing anything to bypass because it even with it set up wrong it would at some point after boiler being off long enough allow pump to turn off .

Providing new boiler stat is wired correctly and functioning i would be looking at where the pump is wired into on the boiler and wether switched live and permenant lives are all in right place..

BYPASS on these must allow at least 1 gallon a minute of circulation.

Pump over run should cut off when temp decreases to 60 degrees C

 

[Johny2b]

Your original fault of pump running constantly is not going to be cured by doing anything to bypass because it even with it set up wrong it would at some point after boiler being off long enough allow pump to turn off .

Providing new boiler stat is wired correctly and functioning i would be looking at where the pump is wired into on the boiler and wether switched live and permenant lives are all in right place..

BYPASS on these must allow at least 1 gallon a minute of circulation.

Pump over run should cut off when temp decreases to 60 degrees C

What it turned out to be is that I missdiagnosed the boiler thermostat (which has built in pump over run stat) which I repleaced. It subsequently found out the replacement new part was faulty.. So put back the old one, and if you removed it form the heatexchanger, and let it cool down - the pump would stop. So this pointed back to what Agile said earlier... The bypass only had a isolating valve not a bypass valve - which was fully open therefore constantly heating the water in the bypass circuit - which meant when the boiler stoped and the overan stat keep the pump running it was pushing hot water into an already hot bypass circuit - therefore continualy running the pump.

The settings on the autobypass valve range from 0.2 - 0.6 mbar of pressure. The chart it gives you shows what you should set it as assuming you know the minimum flow rate (in l/h)
Any ideas?