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

[JasonActs]

Hi all,

Firstly apologies if this is something already covered; I did search the forum prior but couldn't find anything specific that replicates the issues I'm having.

System:
Gravity Fed, cold header tank in loft.
Boiler: Worcester Bosh Greenstar 15Ri
Pump: Archergas 15-60/130 – fitted approx 1 year ago
Diverter Valve: Drayton 3-port
Rads:
7 rads in total – 3 downstairs, 4 upstairs. Bathroom rad is always first to heat whether CH or HW.
Twin entry microbore (cue collective eye roll).
No TRV’s.

The Issue:
- Boiler cuts out after approx 15 minutes on CH.
- All fine with HW, no issues at all.
- On CH the Pump gets quite noisy with a gurgling/gargling/bubbling sound which increases over time.
- Every time I engage CH the boiler cuts-off after approx 15 mins, and even less time(approx 5-8 mins) if I try the CH again shortly after first cut-off.
- No rads get proper Hot except for Bathroom rad.
- Rads downstairs get luke warm. Rads upstairs barely manage a smile and/or remain stone cold.
- Pipes to all rads get warm or hot in the 15 minutes.

Things I’ve tried:

- Bleeding all rads. No obvious air blocks.
- Bleeding/Venting CH pump via bleed screw. Again, no evidence of major air escape.
- Checked CH pump spindle; turns freely (and pump is essentially new).
- Drained system and refilled. The downstairs hallway radiator used for drainage ran clear water out.
- Closing various rads and trying CH. No change.
- Shouting.
- Hit things randomly with a (rubber) hammer.

Things I’ve not tried:

- A plumbing course.
- Posting on a forum.

Would really appreciate any suggestions or advice - wife and I have already been through one winter without heating so it would be worth +10 to avoid another year.

Also, I fully accept this may be something beyond ‘DIY’ but I can’t escape my father’s DIY ethos which led him to scale a roof ladder to fully remove and clean two Velux windows on a pitched roof, or remove a hornets’ nest in the eves with nothing but a can of Raid and some old boxer shorts wrapped around his face.

Thank you in advance.

 

[Hugh Jaleak]

Highly likely to be a circulation issue, Microbore is higher risk for sludge blockages due to its smaller bore. Draining and refilling may well have lost the majority of any Inhibitor that was in there, when you drained the system, was the water clear, or did you get dark, discoloured, even black water coming out?

Chemical Flush may shift some crud, but if the system is that blocked, it may not get round. A Powerflush may be a better option.

 

[Johntheo5]

Does the Boiler cut out "normally" on reaching its target flow temperature and then restart some minutes later without resetting?.
Have a look in the attic while the circ pump starts and stops (get someone to do this for you) and while running...se if any carry over through the F&E cistern vent.
Post a photo of the vent and cold feed setup.

 

[avonmouth]

As above but my experience of twin entry valves are that they are not very good.
Are you capable of removing them and checking the length of copper inside the rad ?.
They often get blocked with sludge.

 

[gas112]

Would not be unusual for the motor in the 3 port to be failing during use and falling back to rest position of Hw or little circuit board in valve failing ... new head would be my choice from your symptoms description

 

[JasonActs]

Thanks v much for replies:

@Hugh Jaleak

- When system was drained the water was fairly clear, and certainly not discoloured/odd enough for us to take note

@Johntheo5

- Boiler doesn’t exactly reset:
- Burner Indicator (Green light) comes ON when CH turned on
- After approx 15 mins, Burner indicator light simply goes off - at which point I then turn CH off via Drayton Programmer/Controls
- MAINS Indicator/Diagnostic Blue light remains on constantly
- Thanks for suggestion to check in loft. Will do and report back.

@avonmouth

- Capable, maybe
- Scared to do so, very

@gas112

- Diverter valve seems to be functioning as normal
- Turn CH on, lever moves to H and remains there
- When boiler cuts out, lever stays on H
- Turn HW on, lever moves to W and remains
- So can probably eliminate the diverter as the issue?

 

[numpty1]

After approx 15 mins, Burner indicator light simply goes off - at which point I then turn CH off via Drayton Programmer/Controls

boiler has reached set temp internally and needs to loose some heat before refiring turning it off does not help the heat,sounds like it is a circulation/dirt issue and external issue,turn it on and leave it run for a couple of hours on 3 or 4 on the stat/dial.

edit. make sure all valves are open on all the rads..

 

[JasonActs]

@numpty1

Thanks - that's definitely something I can try (I'll stick a Columbo film on whilst I wait).

A couple of dumb follow-up queries (sorry):

- Do you mean the stat/dial on the Boiler?
- The Worcester Bosch manual states the temp range is approx 35 - 82 Degrees C but the dial isn't divided into numbers - please see attached image.
- Would about half way be suitable?

- Is it safe to do this even though the pump sounds like a bubbling cauldron of irate hippos?

Many thanks again

 

[Johntheo5]

Mid scale should be OK IMO say 58C/60C, (35+82/)/2, When the boiler cuts out after the 15 minutes, check that the circ pump keeps running continuously, also feel the pipes in/out of the diverter valve, especially the out to the CH and see if its hot, also rad inlets etc. I see you have checked these, any link to your pump, what mode/setting is it on?

 

[gas112]

When the heating goes off and there is still a heating demand does your pump continue to run

 

[JasonActs]

Thanks @Johntheo5

Pump is Archergas - please see attached (

Running on II (Two) Speed.

Going to try the continuous 2 hour CH run later this evening and report back.

 

[JasonActs]

@gas112 - It does, however so far I've been killing the CH v shortly after the Boiler Burner Indicator goes out because:

a) I was concerned about causing damage
b) I don't know what I'm doing
c) wife told me to even though she also doesn't know what she's doing

As mentioned, I'll try keeping it going for longer run and see what happens.

 

[Johntheo5]

This pump appears to have 3 fixed speed and a "Eco" mode which is equivalent to a Grundfos Autoadapt (Proportional pressure control) that I'v never seen to operate properly, just check that it is in fact running in fixed speed 2 .

 

[MickyP10]

Good spot, above, and 'Eco' is the factory default setting.

 

[JasonActs]

Thanks @Johntheo5 - as @MickyP10 says this was a good spot.

For various reasons we won't get into I have a deep seated, some may even say conspiratorially cynical, aversion and attitude to anything labelled or promoted as 'Eco' - so I can definitively confirm I've never used this setting and pump is running on 2 speed.