Tried everything but luke warm radiators

[Actionmainly]

I really at at my wit's end with the heating in my house. So, no matter what I do I cannot get all my radiators to be hot. Luke warm is the best I can get. This has been an issue for a couple of years and we have persevered. What happens is one radiator can be hot but even by turning this down I can't get everything to balance. One simply goes cold and another gets hot. Today I had the heating on and pretty much most radiators were luke warm except a small one upstairs. Even minor adjustments to balance them doesn't affect this. If it isn't this it's cold spots on radiators. Now I've tried bleeding them, I've tried taking them off and forcing water through, balancing them, making sure prrssuenis high enough, I've had a plumber put in some formula (inhibitor?) but nothing has the desired effect.

I have a combi boiler and the hot water is fine, it's just the heating. It's serviced every year and despite a leak a few years ago, the engineers always say it's working fine. I guess the question is do I need to take the plunge and get a new boiler? I just feel like not enough heat is being pushed through the system and it just can't manage to heat all 10 radiators at the same time. Boiler is about 8 or 9 years old and is a Vokera 28 SE. Noone seems to be able to fix this issue so I can only assume it will be the boiler to blame but is there any possibility this could still be something else?

 

[CBW]

Doesn’t sound like the boiler as such. When the heating is on feeling or measuring the flow pipe first would be my port of call, to ensure the diverter isn’t stuck.

 

[Madrab]

Process of elimination. Check how hot the boiler is outputting the flow at, turn all the rads off and starting at the furthest away rad, open that one up and check the temp of the flow at that rad and start to work your way back. Could be a circulation/lazy pump issue.

 

[Actionmainly]

When you say the flow is that the pipe at the lockshield valve side?

Also when you say diverter and lazy pump wouldn't those be parts of the boiler checked on a service?

 

[Johntheo5]

Does the boiler fire continuously even with all rads only lukewarm?
What is the boiler (flow) temperature?
How many rads, how many doubles?.

I can't find the minimum output of this boiler but it seems to be ~ 12kw, if so then the radiators would have to emit > 12kw to allow the boiler to fire continuously and not cycle, Lukewarm rads will not emit 12kw or anywhere near that so ensure the boiler isn't constantly cycling.

 

[CBW]

wouldn't those be parts of the boiler checked on a service?

No they wouldn’t.

 

[Actionmainly]

Does the boiler fire continuously even with all rads only lukewarm?
What is the boiler (flow) temperature?

I can't find the minimum output of this boiler but it seems to be ~ 12kw, if so then the radiators would have to emit > 12kw to allow the boiler to fire continuously and not cycle, Lukewarm rads will not emit 12kw or anywhere near that so ensure the boiler isn't constantly cycling.

So I hear the boiler on and it does continuously make the noise of firing up like a bump noise maybe every 5 minutes until it hits temperature in the room which takes way longer than I would expect it to.

 

[Johntheo5]

Sounds like the boiler is cycling continuously then, what happens is,........the boiler fires up and IF it can start modulating down before it reaches the SP flowtemp+5C it will then continue to run but if the rad demand is lower than the boiler minimum output then the flowtemp will exceed its SP (setpoint) by 5C and the burner will cut out, the circ pump will continue to run and after 3 minutes (anticycle time on most Vokera boilers) the burner will again relight if the flowtemp is at or below SP-5C.

You may have a pump problem, or a partial blockage/restriction in the CH pipework, can you just move the CH temperature control up or down very slightly, it will then flash the SP temperature for a few seconds, note this and watch it and see does it then rise (after the burner fires up) by +5C, the burner will then cut out and remain off for 3 minutes and will then refire, note the flowtemperature when it refires, Would then suggest setting the SP flowtemp to maximum and see does it decrease the cycling.

 

[Actionmainly]

Sounds like the boiler is cycling continuously then, what happens is,........the boiler fires up and IF it can start modulating down before it reaches the SP flowtemp+5C it will then continue to run but if the rad demand is lower than the boiler minimum output then the flowtemp will exceed its SP (setpoint) by 5C and the burner will cut out, the circ pump will continue to run and after 3 minutes (anticycle time on most Vokera boilers) the burner will again relight if the flowtemp is at or below SP-5C.

You may have a pump problem, or a partial blockage/restriction in the CH pipework, can you just move the CH temperature control up or down very slightly, it will then flash the SP temperature for a few seconds, note this and watch it and see does it then rise (after the burner fires up) by +5C, the burner will then cut out and remain off for 3 minutes and will then refire, note the flowtemperature when it refires, Would then suggest setting the SP flowtemp to maximum and see does it decrease the cycling.

The temp on the boiler has always been set to max.

Just to add something this all started a couple of years ago when one radiator just completely stopped heating despite no messing with balancing, having the valves fully open, bleeding it and taking it off and forcing water through. Prior to this it was roasting. By messing about with balancing I have been able to get it warm again but its always been at the expense of another radiator going cooler.

I was kind of resigned to getting a new boiler I'm just concerned if I do I might still have a problem.

 

[Johntheo5]

OK, thanks, if you observe what I suggested then may be able to narrow down the problem, how many rads do you have??.

The max SP is 80C so burner shouldnt cut out until 85C.

 

[Actionmainly]

OK, thanks, if you observe what I suggested then may be able to narrow down the problem, how many rads do you have??.

The max SP is 80C so burner shouldnt cut out until 85C.

I have 10, 5 up and ,5 downstairs.

 

[Johntheo5]

10 should have no problem in satisfying the boiler minimum requirements and a 28kw boiler should have no problems in driving the rads to full temperature in 20 minutes or so, even from stone cold.

Your observations, if you opt to do them, will be interesting.

 

[Actionmainly]

10 should have no problem in satisfying the boiler minimum requirements and a 28kw boiler should have no problems in driving the rads to full temperature in 20 minutes or so, even from stone cold.

Your observations, if you opt to do them, will be interesting.

so system has just fired up from cold and has been on for about 15 minutes. All rads bar 2 have one pipe that is hot to touch. This is a mix throughout the house being the thermostatic valve side or lockshield valve side. On the other side the pipe is either cold or luke warm.

The main thing of note is there isn't a single radiator from the 10, even the smallest that is warm on 100% of its surface. A very small one is about 90% but this is about the limit of what I can get out of it. Basically not a sngle radiator at full temperature and 1 or 2 barely hot at all.

 

[ericmark]

Even if all the lock shield valves are wide open, unless so programmer or thermostat turns the boiler off, the TRV's will one by one control each radiator, will warm up, heat the room then cool down as TRV closes, and next easiest radiator for water to go through heats up.

Setting the lock shields means they all heat up together, and having a wall thermostat means when that room heats up sequence stops.

Should use a diferental thermometer to set up the lock shields, but starting closest to boiler, turn off lock shield wait until pipes cold, then turn back on ¼ turn at a time until you feel a little heat on one pipe then stop, will likely be near enough.

 

[Johntheo5]

And the boiler flowtemperature??. If its 80C and the minimum output is 12kw (does someone know this figure??) then where is the heat going??.