Water not getting hot - boiler cycling

[GasmanxxxR1]

As i said in previous posts, the 15mm pipe is too restrictive and causes the boiler to cycle, 15mm pipe can only carry so much energy and just cant get the heat away from the boiler quick enough

 

[SBDIY]

As i said in previous posts, the 15mm pipe is too restrictive and causes the boiler to cycle, 15mm pipe can only carry so much energy and just cant get the heat away from the boiler quick enough

Yes I understand and see the logic in what you are saying. It doesn't though tally with the fact that it has worked perfectly well, without any problems for 30 years, including the past 8 years since the 15kW Gloworm Boiler was fitted. It would though fit with the pipes being partially blocked with sludge but I have ran some Sentinel through it to clear it out. Maybe I need to try something stronger?

 

[Mickplumb]

Been following your thread was system power flushed when new boiler installed
if not would recommend you get it done with all rads shut hopefully the larger pump will shift any blockage ,get them to fit a magna clean on primary return to boiler while your at it

 

[Ermintrude]

Disconnect flow and return from cylinder , connect cold mains to it and a drain on flow. So water is going up the coil and flush out any pap. I would fit a jet auto air vent aswell.

 

[SBDIY]

As a different line of thought, I mentioned in an earlier post that I wondered if the problem could be something to do with the flow/return Thermistors. Earlier today the boiler shut down with fault F26 which when I checked the manual means Return Thermistor Restriction. Anyone know what that means and could it be relevant to the problem I've got?

 

[GasmanxxxR1]

its indicating you have a problem, its not causing the problem imho, too much difference in temp between flow and return

 

[SBDIY]

its indicating you have a problem, its not causing the problem imho, too much difference in temp between flow and return

Good point - makes sense. I think I will check the two Thermistors though just to make sure they are both responding consistently to changes in temperature. Probably ok but at least eliminates them from the investigation before looking at things more difficult and time consuming.

 

[Nostrum]

The 15mm isn't the issue, there are plenty around with 15mm circ's. They used to do it to balance the coil so it didn't take preference to the heating circuit. It's only 15kw boiler.

i have had a similar problem once before on a heating circuit. The radiators stopped almost overnight. I checked everything and in the end chucked some sentinel x800 jetflo in and within 2 hrs they were working again. Still never found out what caused it and the water was gin clear.

before doing this though, I would isolate a pump valve and carefully crack the nut in the picture with a bin bag underneath to catch the water, this will push water through the bottom of the coil and out the top just to check for blockage or air, the coil could be bend and rising up trapping air although unlikely. Make sure you open the pump valve again.

 

[Nostrum]

Good point - makes sense. I think I will check the two Thermistors though just to make sure they are both responding consistently to changes in temperature. Probably ok but at least eliminates them from the investigation before looking at things more difficult and time consuming.

if there was a thermistor fault you'd get he same issue with the heating...

 

[PlumbBobBob]

Good point - makes sense. I think I will check the two Thermistors though just to make sure they are both responding consistently to changes in temperature. Probably ok but at least eliminates them from the investigation before looking at things more difficult and time consuming.

you shouldn't be messing about inside the boiler, you could make the problems worse.

 

[SBDIY]

The 15mm isn't the issue, there are plenty around with 15mm circ's. They used to do it to balance the coil so it didn't take preference to the heating circuit. It's only 15kw boiler.

i have had a similar problem once before on a heating circuit. The radiators stopped almost overnight. I checked everything and in the end chucked some sentinel x800 jetflo in and within 2 hrs they were working again. Still never found out what caused it and the water was gin clear.

before doing this though, I would isolate a pump valve and carefully crack the nut in the picture with a bin bag underneath to catch the water, this will push water through the bottom of the coil and out the top just to check for blockage or air, the coil could be bend and rising up trapping air although unlikely. Make sure you open the pump valve again.

That's another good suggestion mate and I can do that quite easily, as a non professional, as long as the missus can hold a bin bag 😉.

I have had some X400 in the system a couple of weeks ago and by coincidence today bought some X800 to give it another go.

 

[SBDIY]

you shouldn't be messing about inside the boiler, you could make the problems worse.

Yes, fair enough. I wouldn't mess with a boiler but as an electrical engineer I'm confident to test a Thermistor but you're advice is good and I'll take it.

Also the other point that if it were a Thermistor fault it would happen with the CH also makes sense too.

Thanks.

 

[Nostrum]

I wouldn't trust my misses to hold a door open

 

[Dotty]

Good point - makes sense. I think I will check the two Thermistors though just to make sure they are both responding consistently to changes in temperature. Probably ok but at least eliminates them from the investigation before looking at things more difficult and time consuming.

And to do that you need to be a GSR.

Read the forum rules appertaining to gas appliances.

Thread closed.