Boiler Overheating on cool down.

[Sid79]

Hi,

I'm running an open system with a baxi solo 2 PF40 boiler a Grundfos Selectric UPS 15/50 Central Heating Pump, in an S plan system (I have two separate drive valves).

The pump has been replaced in june of this year. The engineer did a full system drain down to fit etc. He used the wiring system from the previous pump. There were a few airlocks within the system which as far as I can tell have been cleared.

With regards to the boiler, I've had the Overheat and thermostat sensors replaced, along with the fan.

The heating system itself runs perfectly (as far as I can tell) in that all rad's get suitably hot and there are no cold spots within the system. The Hotwater is heated fine too.

I've got two problems currently.

1.) The pump is running continuously
2.) When the system is on its cooling down phase i.e the boiler has shut off there seems to be an influx of air/kettling within the flow pipe to the boiler.

My thoughts with regards to problem 1 is the PCB on the boiler, which controls the pump overrun, from what i've read about this boiler this seems to be a common issue!. I intend to get a gas safe engineer to replace the PCB (also have a look at the wiring too!)

Problem 2 is the one that baffles me.... Could problem 1 with the pump running continuously have a knock on effect and be bringing air into the system uneccessarily?! or is this a separate issue that could require another drain down to resolve?

Thoughts and help appreciated.

Simon

 

[powell30]

Possibly air but you say its overheat so i would guess your bypass is shut too much if manual (gatevalve) or too short a run or auto bypass isn't working.

Never keen on selectric pumps. Come across many which slow too quickly and cause over heat.

 

[Sid79]

Possibly air but you say its overheat so i would guess your bypass is shut too much if manual (gatevalve) or too short a run or auto bypass isn't working.

Never keen on selectric pumps. Come across many which slow too quickly and cause over heat.

Ahh the pump was only put in in june!! There is a manual gatevalve however the valve doesnt have a knob attached to it?! not sure what I would need to open the valve up? (excuse my stupidity on that score!)

Yep when it happens the overheat lamp is lit on the boiler, and prior to that you can hear air/bubbling through the pipe work... however this does happen intermittently!

 

[kevplumb]

not sure what I would need to open the valve up? (excuse my stupidity on that score!)

adjustable wrench

try 1/2 a turn

 

[Sid79]

not sure what I would need to open the valve up? (excuse my stupidity on that score!)

adjustable wrench

try 1/2 a turn

Thanks for that Kev However the valve in question is one of these

http://www.toolstation.com/shop/p17726

stupid question but would an adjustable wrench work!!?

Thoughts muchos appreciated!

 

[kevplumb]

unscrew the top narrow hex first (it might weep a bit)

thats a locksheild you can get a proper key to fit them

 

[Sid79]

unscrew the top narrow hex first (it might weep a bit)

thats a locksheild you can get a proper key to fit them

Ahh smashing thanks for that!! I'm stupid by name stupid by nature

So you would recommend a quarter turn to open it up? will give it a bash!

 

[spraggo]

Hi Sid79
When there is a demand for heating the CH Motorized valve will open and send 240v, from a permanent live through the the orange and grey wires connected to the valve, to the boiler and pump. The HW Motorized will also do this when there is a demand for hot water.
It follows that if either of these valves does not shut when demand is satisfied then the boiler and pump will continue to run. To check this you will need to make sure that there is no continuity through the orange and grey wires to the valve when it is closed, If there is continuity then the valve is faulty.
Regards
spraggo

 

[Agile]

When both motor valves are closed its essential that there is a bypass between the flow and return after the pump but before the motor valves.

You mention a gate valve. Perhaps you know thats been used as the bypass? Nowadays we use an auto bypass and to be more effective they can be fitted across the HW valve so the heat is disapated faster and not wasted.

Assuming this gate valve is the bypasss then opening it ANTIclockwise about 1/4 to 1/2 turns will probably solve your provlem.

Tony



Edited to correct to move valve correctly.

 

[Sid79]

When both motor valves are closed its essential that there is a bypass between the flow and return after the pump but before the motor valves.

You mention a gate valve. Perhaps you know thats been used as the bypass? Nowadays we use an auto bypass and to be more effective they can be fitted across the HW valve so the heat is disapated faster and not wasted.

Assuming this gate valve is the bypasss then opening it anticlockwise about 1/4 to 1/2 turns will probably solve your provlem.

Tony



PS, is there really an o/h lamp on this model?

Tony,

To answer your question about the o/h lamp, on the boiler I have there is! the lights are as follows (L-R) OverHeat, Boiler On, Fan On, Pilot On, Burner On.

I assume the gate valve is the bypass as the engineer who fitted the pump im sure stated as much! Will give the 1/4 to 1/2 turn anticlockwise a shot. I'm guessing the bypass is used once the boiler has switched off and the motorised valves are closed (as far as I can tell both valves work as when I request CH or HW only I get CH or HW only and when they are both requested both seem to be working ok)

To ask a dumb question, would a partially closed bypass cause the air/kettling post boiler switch off?

Simon

Edit as per Tony's message

 

[Agile]

Please edit your posting INCLUDING mine that you have quoted to show that the valve whould be turned anticlockwise to open.

That air comment that you have made is not logical ! If the pump really continues to run then the water flow conditions will not change ???

How can you be sure its still running?

Tony

 

[Sid79]

Hi Sid79
When there is a demand for heating the CH Motorized valve will open and send 240v, from a permanent live through the the orange and grey wires connected to the valve, to the boiler and pump. The HW Motorized will also do this when there is a demand for hot water.
It follows that if either of these valves does not shut when demand is satisfied then the boiler and pump will continue to run. To check this you will need to make sure that there is no continuity through the orange and grey wires to the valve when it is closed, If there is continuity then the valve is faulty.
Regards
spraggo

Spraggo,

Thanks for the reply. The boiler seems to be ok in that when the system is up to temp via the room thermostat or HW thermostat it will switch itself off. The boiler will also cut-out (maybe the wrong teminology) when the internal thermostat hits the correct temp (it does continue running its as normal) The pump on the other hand keeps running and running (like the duracell bunny) even when the boiler is off, the only way to stop the pump is to switch the system off at the mains!

From memory both drive valves are in the middle when the system is off (I may be very wrong on this but i'm not near the system at the mo)

Simon

 

[kevplumb]

Please edit your posting INCLUDING mine that you have quoted to show that the valve whould be turned anticlockwise to open.

 

[Sid79]

Please edit your posting INCLUDING mine that you have quoted to show that the valve whould be turned anticlockwise to open.

That air comment that you have made is not logical ! If the pump really continues to run then the water flow conditions will not change ???

How can you be sure its still running?

Tony

Tony,

re-edited the comment as per your request. WRT to the pump running continously I can hear it humming away!!! The air or kettling?!?! seems to be apparent when the boiler has stopped and is on cool down it takes about 2 mins (roughly) of spluttering then the overheat lamp appears on the boiler.

The pump at this time continues to whirr away even after 8-10 mins have elapsed (which having read the baxi manual (assuming its gospel) is the max time length for the pump to overrun. The overheat cannot be cleared by using the std switch off thermostat wait 10 secs and restart. I have found that if the boiler is re-started by turning up the heating thermostat to re-start the boiler, this as far as I can tell opens the drive valve(s) and the hot water in the flow and return pipes is expelled. I can then reset the overheat using the switch off for 10 secs and back on again. Does this make sense??!

Simon

 

[spraggo]

Hi simon
If you are sure that the MV valves have closed and that there is no continuity between the orange and grey wires on these, the only other cause for the pump to continually run is faulty pump over run stat, which is situated in the boiler. Regarding you noisy pump, have you tried turning the pump settings on the pump down?.