CH 'fires' up for a few mins then cuts out

[Johntheo5]

Where do you change or see what settings the pump is on?. I have a feeling there might not be a Eco setting on that model.
"On CH the Pump gets quite noisy with a gurgling/gargling/bubbling sound which increases over time."
Even though no problems on HW (or refilling) would suggest checking where the vent and cold feed are teed in, if its the conventional (VCP) system where you have the pump on the boiler flow, with, from the boiler, Vent, cold feed, (no more than 150mm apart) then pump, a blockage/partial blockage can occur where the cold feed is teed into the system.

Is this a new problem since the last heating season?.

 

[JasonActs]

CH Test
All Rads open
Pump on speed 2
Boiler Thermostat set approx halfway
Room stat at approx 25 degrees

8:45am
- CH ON
- Boiler Burner Indicator Light ON

9:06
- Burner Light OFF
- Pump still operating but noisy/bubbly

9:19 - Burner Light ON
9:29 - Burner Light OFF
9:37 - Burner Light ON
9:43
- Pump sounds quieter, less bubbly.
-All feed pipes to HW cylinder and going up to loft are hot
9:50 - Burner Light OFF
9:59 - Burner Light ON
10:15 - Burner Light OFF
10:25 - Burner Light ON
10:40 - Burner Light OFF
10:50 - Burner Light ON
11:05 - Burner Light OFF
11:15 – Burner Light ON
11:30 – Burner Light OFF
11:30 – CH turned off manually at controls, test terminated

Boiler
So the pattern emerged as a cycle of:

Burner ON = 15 mins
Burner OFF =10 mins
Repeat

At no point did the boiler shut down/reset or flash any diagnostics.

Pump

Pump continued to run throughout test.
As mentioned after approx 1 hour significant reduction in noise/gargling. The hippos calmed down.
At the end of the test pump remains quieter.

Rads

Various degrees of heat, but wouldn’t say any were PIPING HOT.
One thing of note, but will need to expand further separately...

Entrance Rad
Entrance hallway Rad was cold and pipework barely warm.
Bed 3 Rad
- Upstairs and Directly above this Rad is Bed 3 Rad
- This was reasonably warm
- There has been prev. issues where if Bed 3 Rad = Open then Entrance Rad = Not happy.

Feed Pipes
As mentioned, most pipes connected to pump/diverter/cylinder running hot.

Will try and post pics of the airing cupboard pipework/pump/cylinder setup and specify which are hot, but run out of time now.

Thanks in advance for any thoughts on the above.

 

[Johntheo5]

You seem to be getting some air into the system at least, initially, when it fires up so suugest as before.......
Go to the F&E cistern and get someone to fire up the boiler and watch for any brief burst of water coming from the vent pipe then watch again for any water when the boiler is switched off. With the boiler running normally hold a glass of water under the vent with its end immersed in the water and see does the water level drop in the glass.
You certainly have a circulation problem, with a assumed minimum boiler output of 5kW and a firing time of 15/25, 60%, means the rad outputs are only ~ 3.0kW.

Even though a 3M head should be quite adequate for your system, (normally) just change the pump speed to 3, this should increase the flowrate by over 40% but may result in excessive noise, if so, just return to speed 2.

Try and locate those Vent & cold feed pipes.

 

[JasonActs]

@Johntheo5 - thanks for staying with this and apologies for belated response - have been away for a few days.

Vent Pipe Tests

Pre-testing: Vent pipe that runs over cold water tank is dry as a bone, inside pipe and externally, indicating that no water has passed through recently.

- CH ON
- No activity from Vent pipe. Just sits there looking stoic and despite my offering the number of a very good therapist it refuses to vent.
- CH runs for approx 15 mins and Boiler Burner OFF (see prev. test)
- No activity from Vent pipe.
- Wait 10 mins - Boiler Burner ON.
- No activity from Vent pipe.
- Bled a few rads whilst Boiler Burner On - no air escape, and (clear) water comes out almost instantly.
- CH turned off at controls.

Total time of this test = approx 30 mins.

So even with the fairly confident assumption of air in system it doesn't yet want to exit via the vent.

Whilst boiler running did also place pint of water in/under vent pipe end. No suction noted.

After test ending did also place pint of beer under my face. Full suction noted.

 

[Johntheo5]

Still looks like a circulation problem.

Did the rads heat up properly just after the circ pump was replaced, why was the pump replaced?.

As suggested, you might, just, even briefly. change to speed3, if noise increases, return to speed2

Can you see where the cold feed & vent join up, see post #16.

Can you, sometime turn up the HW cyl thermostat to say 70C, then fire the boiler with both CH & HW requested, see if rads then heat up and burner run for more than ~ 10 minutes, return cylinder stat setting to its original, normally 60C after test completed.

 

[JasonActs]

@Johntheo5

- Pump replaced approx 1 year ago because (very) old Grundfos pump spindle was getting jammed frequently.
- CH was fairly lacklustre prior to pump change but did essentially operate and boiler/burner remained on; after new pump install CH never on long enough to properly gauge results ;/
- During CH Test Post #17 I did switch pump to 3 speed at approx 10:50am. Burner cut off slightly sooner than on 2 speed. Returned pump to 2 speed.

- Cold feed/vent join - will try to work out, but obv. not being a plumber all I see is pipes and pipe dreams of being as knowledgeable as a plumber.

- HW cyl currently on approx 60 - will raise to 70 and try CH/HW simultaneous (something I had intended to try) and note rads/burner status.

Thank you John.

 

[JasonActs]

CH & HW Demand Test

HW Cylinder set to 70 degrees (was 60 prev.)
HW & CH turned ON at controls.

- Diverter Valve moves to M.
- At 22 mins boiler Burner still ON.
- Run HW tap: water is warm/hot but not scolding hot.
- Rads behaving as per prev. tests i.e. some tepid, some hotter,
- Entrance Rad cold inc. pipework, as prev. tests.
- At 30 mins boiler Burner still ON.
- At 30 mins turned HW Demand OFF at controls.
- CH Demand remains on.
- Diverter valve moved from M to H.

- Restarted my stopwatch.

- At 4m 10s Boiler Burner OFF.
- CH Demand remains on.
- At 15 mins, Boiler Burner had not come back ON.
- In prev tests, after Burner OFF it would generally come back ON after 10 mins if demand remained.
- CH turned off at controls.
- HW Cylinder thermostat returned to 60 degrees.

 

[Johntheo5]

Next time the HW cylinder is being heated feel the coil inlet and return piping, the inlet will be fairly high up on the side of the cylinder and the return directly below it near the bottom, the inlet should be very hot, at the boiler flow temperature and the return should be hot but not lukewarm, if lukewarm might point further to circulation issues , its unlikely to be the pump but cannot entirely be ruled out, otherwise possibly restriction where the cold feed is teed in to the system.
If you had/have one of those cheap ~ £15 plug in energy monitors then by sticking a 3 pin plug on the pump cable and plugging it into a extension lead, its easy to derive a reasonable circulation flowrate from the pump power.

 

[MeldrewsMate]

Once you get the pump to run at the set speed turn off the towel rad fully, then report back on the CH effectiveness. This may be a simple case of poor heat distribution caused by poor balancing.
With microbore pipework you may have to run the pump at speed three.

Does the water pipe (cold feed) from the loft mounted F&E tank (usually 15mm) join the system just before the pump inlet?
Is the pump installed the correct way around?
Is the vent pipe to the F&E tank joined to the system close to the water pipe (cold feed)?

Photos often help

 

[JasonActs]

If you had/have one of those cheap ~ £15 plug in energy monitors

I only have one energy monitor and if i tried sticking a 3 pin plug in her this would be my final post...

 

[JasonActs]

Once you get the pump to run at the set speed turn off the towel rad fully,

Thanks @MeldrewsMate - no towel rad in the circuit, just the Bathroom Rad first in line which gets piping hot with both CH and HW demand irrespective of other results/rads.

Should I try closing this Rad once pump running as a test?

Does the water pipe (cold feed) from the loft mounted F&E tank (usually 15mm) join the system just before the pump inlet?
- Will check and report

Is the pump installed the correct way around?
- Even though Pump is inverted (upside down) I'd have to go with yes, as it was inverted previously when all working and presume HW would have issues if new pump incorrectly fitted?

Is the vent pipe to the F&E tank joined to the system close to the water pipe (cold feed)?
- Will check and report

Will get some photos...

 

[Johntheo5]

The easiest way to check the above (probable) positions is to locate the 3 way mid position valve, you should then find the pump fairly close to this with the pump arrow pointing towards the MPV, you should find a (the) 15mm cold water feed a little further back and, not more than 150mm further back, the 22mm Vent, these will/should all be on the boiler flow (hottest) pipe.

 

[JasonActs]

Going to have to come back to this in a bit as have a flood (excuse the pun) of other lifey things need sorting, but wanted to thank @everyone for their replies and advice so far - it is really appreciated.