Flow Temp Rising Too Quickly - Fix?

[Johntheo5]

My radiators are all TRVs set to about 3. Bathroom rail has no TRV - that is open so it gets but not fully. Rad where central thermostat is fully open.

Any relevance?

It probably should be enough to have one fully open and the other partially open, it depends on how fast the boiler ramps down (modulates) after firing up at ~ (25*60%),15kw, range rating the boiler to 9kw or whatever will not stop this initial fire up setting.

How do I check AAV?

You can't, need to be gas registered.
Have you tried firing up yet

 

[dilalio]

#9 looks like a magnetic filter to me!

He posted the photos whilst I was typing my #10

 

[John Smith Esq.]

So I cleaned the filter out and gave it a good few flushes so ended up with half a bucket full. Quite a lot of black sediment in the water since it has never been emptied in the 2.5 years I've lived here, and possibly not before that.

Refilled the system up to the usual 1.25 bar.

Did the air purge again, which sent a noise to a particular tall radiator which is close to the boiler and has its own circuit off the main pipes.

Decided to go around and bleed radiators and the filter. The filter let a little bit out. None of the radiators needed bleeding apart from one. The tall one near the boiler. It had so much air in it that I was there for about five mins bleeding it and the boiler pressure was at zero once I finished. Repressurised the system and then let out what air was left in that radiator.

Could that radiator have been receiving all the air when I've done these air purges? Or did it end up with a load of air in it earlier when I cleaned out the filter? Or, has it been full of air for a long time and I didn't realise? I am in the habit when I bleed radiators of immediately stopping once I see some water. But that tall one let some water out earlier and then loads of air, so perhaps I've mistakenly not bled it in the past thinking it wasn't needed...

Seems weird how that radiator ends up with all the air. Any ideas why? See photos. The two skinny pipes lead to that one radiator.

Boiler is running now so let's see if it stays at 53C once it gets there...

 

[fixitflav]

So I cleaned the filter out and gave it a good few flushes so ended up with half a bucket full. Quite a lot of black sediment in the water since it has never been emptied in the 2.5 years I've lived here, and possibly not before that.

Is there inhibitor in the system? If not, put some in pronto! Adding it via the filter is the easiest way

 

[dilalio]

Tall rads notorious for catching a lot of air. I saw in your earlier photos that you had 2 x 15mm branches off the flow and return to the boiler and knew they were to feed an added radiator. The 2 x 15mm ballofix isolator valves on the pipes should not be used on heating circuits - they are too restrictive and also leak for fun.

Tip for bleeding tall rad is to turn them off before you do it, using both valves but one would do. If you close both, remember the number of turns on the LS.

It sure sounds like air was/is your issue, with pockets of it getting into the hex. Any money that the AAV in the boiler has been screwed down to off position.

 

[John Smith Esq.]

Is there inhibitor in the system? If not, put some in pronto! Adding it via the filter is the easiest way

Yeah, was some put in previously. I'm guessing sediment stuff happens regardless. But this may also have been a load of old sediment.

 

[Johntheo5]

Boiler is running now so let's see if it stays at 53C once it gets there...

It will stay running at 53C providing the heat load (rad TRVs throttling in) stays higher than the minimum output of the boiler, once the heat load falls below the boiler minimum output then the return and flow will start rising until the flowtemp rises to SP+5C, (53+5), 58C, the burner will then trip, the circ pump will continue to run, when the anticycle time has elapsed and providing the flowtemp is < SP-5C. (53-5), 48C, then the boiler will refire and hopefully get away after one recycle, if the flowrate is say 12LPM then the flowtemp on refiring must have fallen to 37C or lower to avoid the burner tripping again at 55C while the ignition settings are held at ~ 15kw, thats the acid test. Generally speaking, the longer the anticycle time the better as it gets the flowtemp well down.

 

[John Smith Esq.]

Tall rads notorious for catching a lot of air. I saw in your earlier photos that you had 2 x 15mm branches off the flow and return to the boiler and knew they were to feed an added radiator. The 2 x 15mm ballofix isolator valves on the pipes should not be used on heating circuits - they are too restrictive and also leak for fun.

Tip for bleeding tall rad is to turn them off before you do it, using both valves but one would do. If you close both, remember the number of turns on the LS.

It sure sounds like air was/is your issue, with pockets of it getting into the hex. Any money that the AAV in the boiler has been screwed down to off position.

Thanks for this.

Why would the AAV have been closed? Can this damage the boiler or is it more a case of knock on effects like this air issue?

When I do an air purge then, is that air going into the radiators (that tall one) but should be going out of a vent in the boiler?

Should I have those valves you mention replaced then?

Funnily enough, that tall radiator is now performing better than ever! I knew there was something not right.

The flow temperature is now working more normally. It stayed on 53C for a little while, but did then rise to 54C and then after a little but went to 55C. At that point the cycle ended and it started falling again. Just to be clear, the temperature isn't flying up past the set flow temp, it is doing it in a slow and gradual way. Am I right in thinking it should go to 53 and stay there since I have that as the set temp?

 

[Johntheo5]

Thanks for this.

Why would the AAV have been closed? Can this damage the boiler or is it more a case of knock on effects like this air issue?

The flow temperature is now working more normally. It stayed on 53C for a little while, but did then rise to 54C and then after a little but went to 55C. At that point the cycle ended and it started falling again. Just to be clear, the temperature isn't flying up past the set flow temp, it is doing it in a slow and gradual way. Am I right in thinking it should go to 53 and stay there since I have that as the set temp?

AAVs should be called AWVs, automatic water vent(s), they generally either get blocked up or continually keep dribbling water, hence shut off, very often.

If your boiler setpoint is set to 53C then the burner shouldn't trip until (53+5), 58C, the probable reason for not reaching 53C rapidly is because you have the output clamped to ~ 9.0kw.

 

[John Smith Esq.]

It will stay running at 53C providing the heat load (rad TRVs throttling in) stays higher than the minimum output of the boiler, once the heat load falls below the boiler minimum output then the return and flow will start rising until the flowtemp rises to SP+5C, (53+5), 58C, the burner will then trip, the circ pump will continue to run, when the anticycle time has elapsed and providing the flowtemp is < SP-5C. (53-5), 48C, then the boiler will refire and hopefully get away after one recycle, if the flowrate is say 12LPM then the flowtemp on refiring must have fallen to 37C or lower to avoid the burner tripping again at 55C while the ignition settings are held at ~ 15kw, thats the acid test. Generally speaking, the longer the anticycle time the better as it gets the flowtemp well down.

Interesting! Thanks for explaining.

This rings true with what I've been seeing on the display. 48 and 58 are typical trigger points.

So are you saying this is all normal? Basically, some radiators are wanting less heat after a while because of TRV settings so the boiler inevitably drifts above the set flow temperature and has trigger points to stop and lower back down again? No problem? I thought it should just stay on 53C and these 341 error messages relayed to this.

So what would you do with these settings to get a more efficient and cost effective outcome?

2.3B (anti fast cycle time)

Current setting: 5 mins. (Options are 3mins - 45mins).

2.3C (anti fast cycle flow temp)

Current setting: -6 (Options are -30 to 0)

2.9E (flow turbine signal delay)

Current setting: 2 (options are 2 - 12)

 

[John Smith Esq.]

AAVs should be called AWVs, automatic water vent(s), they generally either get blocked up or continually keep dribbling water, hence shut off, very often.

If your boiler setpoint is set to 53C then the burner shouldn't trip until (53+5), 58C, the probable reason for not reaching 53C rapidly is because you have the output clamped to ~ 9.0kw.

So I need the AWV checking and possibly fixing or is the situation ok based on what I've described?

Also, would you say I am wasting gas by using the 9KW setting? I assumed this is a money saver.

 

[Johntheo5]

Interesting! Thanks for explaining.

This rings true with what I've been seeing on the display. 48 and 58 are typical trigger points.

So are you saying this is all normal? Basically, some radiators are wanting less heat after a while because of TRV settings so the boiler inevitably drifts above the set flow temperature and has trigger points to stop and lower back down again? No problem? I thought it should just stay on 53C and these 341 error messages relayed to this.

So what would you do with these settings to get a more efficient and cost effective outcome?

2.3B (anti fast cycle time)

Current setting: 5 mins. (Options are 3mins - 45mins).

2.3C (anti fast cycle flow temp)

Current setting: -6 (Options are -30 to 0)

2.9E (flow turbine signal delay)

Current setting: 2 (options are 2 - 12)

I would try option 2.3C, set it to say - 15C, and see how it goes, the burner then will not refire until the flowtemp falls to 38C even with the elapsed 5 minute anticycle time, its a very good option IMO and should be a standard feature on all gas fired boilers.

 

[Johntheo5]

So I need the AWV checking and possibly fixing or is the situation ok based on what I've described?

Also, would you say I am wasting gas by using the 9KW setting? I assumed this is a money saver.

Maybe install a AAV where you can access it yourself, someone posted a photo quite recently of one that you can remove without draining down the system or installing a isolating valve.

You certainly arn't wasting gas by range rating to 9.0kw.

 

[John Smith Esq.]

Maybe install a AAV where you can access it yourself, someone posted a photo quite recently of one that you can remove without draining down the system or installing a isolating valve.

You certainly arn't wasting gas by range rating to 9.0kw.

Thanks pal!

So installing a new one outside boiler will do the job of the possibly seized one inside the boiler?

Do you know how I clear these D4 341 error messages? Pressing reset and holding it etc doesn't get shut of it. So I don't know if it is a current problem or not regarding the temp rising too fast.

 

[John Smith Esq.]

I would try option 2.3C, set it to say - 15C, and see how it goes, the burner then will not refire until the flowtemp falls to 38C even with the elapsed 5 minute anticycle time, its a very good option IMO and should be a standard feature on all gas fired boilers.

Does this mean things will cool down more in the house?

Does increasing the time for 2.3b basically achieve the same thing? - forces the boiler to wait longer between firing cycles?