Boiler not starting after drain down

[Rosscardwell]

Advice please.
I drained my open system to add x800 a couple of weeks ago and all ran smoothly. Last night I drained it all out, cleaned the tank and added inhibiter but when I have filled the system add bled all the radiators, the boiler won’t stay on.
All radiators are full, no more air coming out when bled. The pump is a grundfos ups3 and as far as I can see it is self venting as no bleed screw on there.
Have I created an airlock else where?
The boiler fires for a minute then shuts down and keeps repeating every 5 minutes or so.
I’m happy to get a plumber out but I don’t understand why everything worked fine last time I drained but now it hasn’t worked.
Cheers

 

[ShaunCorbs]

Air locked try leaving it on hot water only for an hour

 

[John.g]

If oil fired and no air vent on the boiler top then you can release any air by turning the PRV knob slowly anticlockwise to release any air, slight risk involved of PRV leaking afterwards though. The boiler can be off while doing this.
Its also recommended to set the UPS3 on full speed for 10 minutes but with a open vent system I wouldn't dream of leaving it run for 10 minutes, perhaps a few minutes at most as you run a big risk of introducing more air into the system.

 

[Rosscardwell]

Air locked try leaving it on hot water only for a

If oil fired and no air vent on the boiler top then you can release any air by turning the PRV knob slowly anticlockwise to release any air, slight risk involved of PRV leaking afterwards though. The boiler can be off while doing this.
Its also recommended to set the UPS3 on full speed for 10 minutes but with a open vent system I wouldn't dream of leaving it run for 10 minutes, perhaps a few minutes at most as you run a big risk of introducing more air into the system.

 

[Rosscardwell]

Thanks for that. It is just a regular gas boiler though.
When the pump was installed it was left on max speed and has been fine for over a year.

 

[John.g]

You must have a very well installed OV system then IMO, presume you have checked that the circ pump is actually starting and continuing to run when the boiler cuts in/out?

 

[snowhead]

Does any of the pipework out of the boiler get hot / warm?
Do either of the pipes at the pump get hot / warm?

 

[Rosscardwell]

You must have a very well installed OV system then IMO, presume you have checked that the circ pump is actually starting and continuing to run when the boiler cuts in/out?

Does any of the pipework out of the boiler get hot / warm?
Do either of the pipes at the pump get hot / warm?

You must have a very well installed OV system then IMO, presume you have checked that the circ pump is actually starting and continuing to run when the boiler cuts in/out?

Yes, the pump seems to working fine. Carries on when boiler cuta out

 

[Rosscardwell]

Does any of the pipework out of the boiler get hot / warm?
Do either of the pipes at the pump get hot / warm?

Hi, yeah the pipes coming out of boiler and either side of the pump are all hot. The boiler wants to work but just cuts out.

 

[John.g]

Can you increase the boiler flow target (setpoint) temperature to max from its present setting of? and ensure all systems are calling for heat, if the system is cool/cold then it should normally take 15/30 minutes before boiler cut out at setpoint temperature.
Does the boiler display the temperature?.

 

[Rosscardwell]

Can you increase the boiler flow target (setpoint) temperature to max from its present setting of? and ensure all systems are calling for heat, if the system is cool/cold then it should normally take 15/30 minutes before boiler cut out at setpoint temperature.
Does the boiler display the temperature?.

I did try that last night. Set to max with all rads trv’s at max. Boiler runs for 30secs or so before cutting with gargling noise. Only radiator next to boiler slightly warm. Thanks

 

[John.g]

DHW system open as well?.
Definitely points to air in the system, if so, then running at full speed on that UPS3 won't help matters as its > 6M and will probably cavitate at that setting, would suggest changing to speed1 (4.2M) until problem resolved,
where is the pump installed, is it at the boiler or up high in the hot press or whatever and is it installed on the flow from the boiler?, a photo would help.

 

[Rosscardwell]

DHW system open as well?.
Definitely points to air in the system, if so, then running at full speed on that UPS3 won't help matters as its > 6M and will probably cavitate at that setting, would suggest changing to speed1 (4.2M) until problem resolved,
where is the pump installed, is it at the boiler or up high in the hot press or whatever and is it installed on the flow from the boiler?, a photo would help.

I appreciate this mate. I am work now though can’t upload any photos. The pump is in the airing cupboard next to the bathroom and the boiler is in the bathroom but I couldn’t tell you which pipe it is on.
I expect I’ll be getting a pro out as will need it working for the weekend. It’s just frustrating as it’s a job I already diD correctly a couple of weeks ago

 

[John.g]

No problem, if you do decide to give it another go this evening then post a photo and give us a shout.

 

[Rosscardwell]

No problem, if you do decide to give it another go this evening then post a photo and give us a shout.

My girlfriend just sent me some photos but she thinks she’s a comedian so excuse her toes!

Do these offer any more clues?

 

[John.g]

Was/is the boiler/pump still "running" when the photos were taken?, the pump LEDs don't seem to conform to any normal settings, or/and when you were looking at it were the LEDs, one green+two yellow, illuminated, showing constant (full speed ) curveIII which you say the pump was set to.
I have included the pump photo "right way up" to compare more easily.

 

[Rosscardwell]

Was/is the boiler/pump still "running" when the photos were taken?, the pump LEDs don't seem to conform to any normal settings, or/and when you were looking at it were the LEDs, one green+two yellow, illuminated, showing constant (full speed ) curveIII which you say the pump was set to.
I have included the pump photo "right way up" to compare more easily.

View attachment 73618

The pump was running at level 1 when photo taken but boiler not ignited. She changed the speed as you suggested from fulll (1 green, 2 orange lights)

 

[John.g]

Ok, fine, the illuminated LED is probably being reflected in the next one so leve1 it is, its more than likely that this won't cure the problem on its own, most of the OV problems that occur after refilling after a full drain down seem to occur in systems like yours where (I think ) the pump is pumping downwards, no problem once air has been vented, the trick is how to get rid of it.
Suggest turning the temperature setting back down to ~ 12 oclock position but wouldn't let the boiler cycle on/off all day like this, of course the problem may not be air ingress but in the absence of any temperature gauge?? difficult to say.
If the boiler was cutting out on its boiler stat then the flow pipe immediately after the boiler should have been almost untouchable with the setpoint at max which is probably around 80C.

Also make sure that the HW cylinder is calling for heat, motorized valve open.

 

[John.g]

You probably did but any motorized valves should be latched open manually when refilling the system.

 

[Rosscardwell]

You probably did but any motorized valves should be latched open manually when refilling the system.

You probably did but any motorized valves should be latched open manually when refilling the system.

Yeah I did set it to manual. It needs to be on auto now though right?

 

[John.g]

That correct, it looks like you have "only" one, if so, then it will/should be a mid position valve where you can have DHW only on, CH only on or DHW&CH on. Maybe, as suggested in post #2, select HW only on the programmer, and run like this and see if the system clears/boiler runs continuously. I presume the HW cylinder is cool/cold now?.

 

[Rosscardwell]

That correct, it looks like you have "only" one, if so, then it will/should be a mid position valve where you can have DHW only on, CH only on or DHW&CH on. Maybe, as suggested in post #2, select HW only on the programmer, and run like this and see if the system clears/boiler runs continuously. I presume the HW cylinder is cool/cold now?.

I apparently need a new 3 way port but not sure how this could have failed just from draining and refilling the system…

 

[John.g]

Interesting, since the pump continued to run with boiler off, one might have thought that it would have heated either the HW cyl or the rads if stuck in one position or the other, anyway if this fixes the problem, fine.

 

[Rosscardwell]

Interesting, since the pump continued to run with boiler off, one might have thought that it would have heated either the HW cyl or the rads if stuck in one position or the other, anyway if this fixes the problem, fine.

Yeah I thought the same but he said it was letting heat through but the pipes were all hot last night. Any way he’s just left and the same issue is still there with the boiler but he said it is air locking and will come through by the morning. Which is kind of what I thought the issue was anyway, not a new £200 3 way port…

 

[John.g]

Has he changed the complete valve including the actuator or just the actuator?.
If the former, he may have left the old one with you and you can at least just play with it manually and see if the ports are communicating properly you as you manually operate the lever.

 

[John.g]

Can you take a photo sometime of where the vent and cold feed are located, if you move back along the top of your pump you should see a sort of H, where coming from the boiler you should have vent, cold feed then pump suction (on the "top" in your case) the vent and cold feed should be within 150mm of each other.
With the pump running, have a look into the feed & expansion tank and look for any movement in the bottom of the tank or any sign of pump over through the vent.
If there is/was even the slightest restriction in the short section of piping between the vent and cold feed then this will lead to air ingress through the vent when the circ pump starts and stops and you can sometimes see this happening if you watch the vent while someone stops/starts the boiler, allow a few minutes for pump overrun when the boiler is stopped.
Another sign of long term pump over/back is a very dirty Feed & expansion tank.

 

[Rosscardwell]

Can you take a photo sometime of where the vent and cold feed are located, if you move back along the top of your pump you should see a sort of H, where coming from the boiler you should have vent, cold feed then pump suction (on the "top" in your case) the vent and cold feed should be within 150mm of each other.
With the pump running, have a look into the feed & expansion tank and look for any movement in the bottom of the tank or any sign of pump over through the vent.
If there is/was even the slightest restriction in the short section of piping between the vent and cold feed then this will lead to air ingress through the vent when the circ pump starts and stops and you can sometimes see this happening if you watch the vent while someone stops/starts the boiler, allow a few minutes for pump overrun when the boiler is stopped.
Another sign of long term pump over/back is a very dirty Feed & expansion tank.

 

[Rosscardwell]

Is this the point you mean?
The boiler is fully back to not working so I don’t think what the plumber did has fixed anything so that’s annoying. I never thought there was a problem the 3 way port as was working fine before I drained it.

I will have a look up in the loft tomorrow but I really think he missed the air lock Issue.

 

[John.g]

Yes I would think that H is the vent and cold feed.

Annoying all right but problem still the same.

Even if unlikely Its possible that a load of sludge has now lodged in the pump internals or/and the valve ports but hopefully not in the boiler Hx after that clean out even if thoroughly flushed down afterwards.

Did he replace the whole mid position valve, if so then he would have had to drain or partially drain down the system.??

Short of getting him back I would suggest isolating (switch out) the boiler, shut the pump isolating valves and loosen the pump (bottom) outlet pipe connection, re open the pump inlet valve fully and see can you vent any air, maybe do the same in reverse, I would probably remove the pump to inspect it for sludge build up but worth trying the above first?.