GlowWorm 18HXI intermittent hot water

[jaytc2003]

Hi I have the glowworm 18hxi boiler and occasionally (more frequently recently) we get only lukewarm water when we run the hot taps etc. This seems to happen more frequently if we have the ch turned up (ch is always on at about 18c sometimes if it is cold we turn it up)

The boiler runs 12 rads, 8 of which are regular size and 4 are a smaller size, central heating appears fine as all rads heat up when required etc. The pressure in the system is within spec as well, and the boiler fires up when needed and doesnt show any errors.
Water pressure from the taps seems fine as well so I dont think there is any blockage

There are 2 honeywell motorised valves in the system, one appears to be the hot water side and has no resistance in the lever between auto and manual which I believe is correct as hot water is set to be constantly on, the other valve on the ch side does have resistance if the stat temp is set higher than the room temp.

To check the valves (they have the dimple on so can be swapped without bleeding the system) I have swapped them across the circuits (with wiring) and the same happens (resistance and no resistance same as above) so I think I can remove the valves from the fault. The pump a grundfoss (dont know model) appears to work as well on all 3 speed settings (currently on the lowest setting).

I tried to reset the boiler, and when I turn it on apparently it is supposed to show a pressure reading but it doesn't

Anyone any ideas on what the problem could be?

Cheers
James

 

[Agile]

What exactly did you swap?

What about the room stat and the programmer?

Tony

 

[jaytc2003]

Hi Tony, I swapped the motorised valves over to check to see if one was faulty or not, but it appears that they are both operating correctly.

 

[lightning]

Check cylinder stat is on 60 degrees, does boiler fire up when programmer set on hot water only
move m/v to manual does this fire boiler

 

[jaytc2003]

Hi Lightning, boiler seems to fire fine. If I move the lever to manual it makes no difference. The valve itself is warm/hot similar temperature to the pipes that it is connected to.

I just set it so that the ch was off and only hot water was on, I turned the boiler temp right up (should be about 80 max however only hit 78 but boiler fired ok) got hot water which I ran for a good few minutes with no noticeable temp drop, however I then turned on the ch again, and turned the room stat upto about 25c. The temp in the boiler dropped rapidly by about 20 degrees and wouldnt climb. Water temp did appear to go a bit cooler but still hot. I tend to have the boiler temp around about 50 so if I am getting such a big drop when the ch is on then it could I suppose be dropping to around about 30 ish.

It seems as though the boiler cannot supply adequate demand although it does work fine most times and has worked flawlessly in the 5 years that it has been installed (new build), its just recently that we are getting this more intermittent problem.

Boiler has been serviced every year as well.

 

[jaytc2003]

just remembered, sometimes when the problem occurs, there is a gentle banging noise that comes from the boiler at the same time

 

[Agile]

Have you ever had the boiler serviced?

What do the boiler flow and return pipe temperatures feel like?

Same question on a selection of rads?

It sounds as if the pump impeller may be blocked. Are you competent to remove the pump head and inspect it?

Tony

 

[jaytc2003]

Hi Agile, boiler has been serviced every year.

There are only 2 pipes on the boiler??? A plastic pipe that connects to a plastic little tank on the underside of the boiler, and then a metal pipe which is connected on the underside if the boiler also (looks like it has a valve of some kind in the pipework)

When you say the pump impeller may be blocked, do you mean on the grundfoss pump or something on the boiler?

Rads heat up fine (I can turn them all up and they heat up perferctly)

thanks