J
joop1977
Obviously a circulation problem,to suggest i'ts an oversized boiler is complete rubbish!
Replacement radiator is colder at bottom than it is at top.
- Thread starter fluff29
- Start date
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Boiler runs for 20 minutes and still no acceptable temp difference. Cycling comes later. Rads have not heated in initial 20 minutes. Most boilers would be able to do this in around 5 minutes.
DH, While I agree summer heat load may well be 6kw (half the power needed when boiler just ticking over) what I would expect is temperature gradient in single figures at the radiators and F+R pipe at the boiler especially when the lock-shields were fully open. Boiler runs for 20 minutes but still the temperature gradient across the F+R is 43 degrees. I see that as lack of circulation to the rads except one in the bathroom (I wonder if this one is a ladder type rad just about sitting on top of the boiler). In 20 minutes nearly all radiators show large temperature differential. Boiler is fitted with (most likely) 15/60 pump, has on tap 28kw of heat energy. I would be looking at this heat and pump power to throw deluge of water at the rads unless this was being short circuited at the diverter. This can obviously by checked by taking temperature readings at boiler isolating valves and connections at the main heat exchanger.
Let me digress for a moment. On a Vokera Flowmatic, the front-end (part number 0159), has a spring that distorts and then breaks up. To a heat demand, the boiler functions correctly but there is poor circulation to the radiators as most of the circulation is through the hot water heat exchanger, thus the burner keeps shutting down with rads remaining cool to tepid. Taking temperature reading as requested above would give us direction instead of suggesting boiler be maladjusted (Tony’s idea) as no mention of min setting is found in the MIs. Even holding flow pipe in one hand and return on the other would allow one to make judgement on temperature differential- no need for dual probe thermometers here.
DH, the burner is going out as the ‘cold’ water on the return side of the rads is not getting to the boiler in sufficient amounts to temper the water in the heat exchanger. Sensor on the output of this heat exchanger tells the controls to shut down the burner thinking rads are toasty.
Fluff, why do you want the tap running whilst checking the temperatures on the boiler? I seem to have overlooked the reason for this.
DH, I follow your posts with interest but am a little surprised at some of the thoughts on this thread. I can take the 'bucket test' with a pinch of salt but your posts are usually educational when it comes to calculations and solid information (Thanks to Scruff for direction here)
Unfortunately, as often happens we are only getting a part of the story.
As to why the OP was messing up the cycling tests by turning on the hot tap is anyone's guess.
The diverter might be leaking but as far as we know there might be a rad which is taking far too much flow. However a microbore is largely self balancing. I still dont gather why balancing does not sort out the flow to the cooler rad.
Even a simple hand assessment of flow and returns would be informative.
Tony
As to why the OP was messing up the cycling tests by turning on the hot tap is anyone's guess.
The diverter might be leaking but as far as we know there might be a rad which is taking far too much flow. However a microbore is largely self balancing. I still dont gather why balancing does not sort out the flow to the cooler rad.
Even a simple hand assessment of flow and returns would be informative.
Tony
I haven't read every single post, but a few things caught my speedreading eye:
If you use cleaning chemicals, you have to flush them OUT. The instruction missed that bit.
Forget about the boiler being oversized. You do not need a new one. You should be able to get piping hot rads.
Leave the hot tap OFF while you're testing, If the boiler detects a tap water flow it turns the heating OFF.
Start with the hot water having been off for a good while, everything cold. Run the heating. The blue thing is the heat exchanger foir the tap water, It should NOT get hot, feel it. If it does it's like a short circuit on your heating:
If you use cleaning chemicals, you have to flush them OUT. The instruction missed that bit.
Forget about the boiler being oversized. You do not need a new one. You should be able to get piping hot rads.
Leave the hot tap OFF while you're testing, If the boiler detects a tap water flow it turns the heating OFF.
Start with the hot water having been off for a good while, everything cold. Run the heating. The blue thing is the heat exchanger foir the tap water, It should NOT get hot, feel it. If it does it's like a short circuit on your heating:
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Your speed reading let you down!
We'll agree to differ on that one.
But the OP noted a difference between having the tap OFF and having it slightly open, but not enough to turn the heating off.
If it is acting as a short circuit, what would the effect be and why?
Yes there is - CH CAP, I'd guess.
But without MFRS instructions on it we can't recommend anyone goes twiddling.
It depends what the problem really is and how the boiler works exactly. It could help or hinder.
I must admit I'd try it, but that's with measuring temps and gas pressures inside the boiler as I did it, knowing what other boilers do, ...
It could always be put back where it was if it was carefully marked.
I suspect the problem lies elsewhere, because it isn't usually a problem.
But without MFRS instructions on it we can't recommend anyone goes twiddling.
It depends what the problem really is and how the boiler works exactly. It could help or hinder.
I must admit I'd try it, but that's with measuring temps and gas pressures inside the boiler as I did it, knowing what other boilers do, ...
It could always be put back where it was if it was carefully marked.
I suspect the problem lies elsewhere, because it isn't usually a problem.
There certainly is another problem.
But reducing the CH power will reduce cycling and increase the proportion of time the boiler is firing and delivering heat.
I always range rate boilers because they work better that way.
Tony
But reducing the CH power will reduce cycling and increase the proportion of time the boiler is firing and delivering heat.
I always range rate boilers because they work better that way.
Tony
If the problem is due to a blockage in the system, why do the indicator lights not show this?
From MI's:
A Illuminated continuously and B flashing - Pump fault or restricted flow
The OP has said that there are no unusual lights showing.
From MI's:
A Illuminated continuously and B flashing - Pump fault or restricted flow
The OP has said that there are no unusual lights showing.
Once the tap Hex is hot, hot water will be speeding up the heat rise in the boiler, shortening the cycle. The return pipe wouldn't get hot outside the boiler.
I know what you mean, it's worth a try, but it often makes little or no practical difference. (Vaillants of course are pretty extreme!) We all see lots of combis with 3 rtads which all get perfectly hot.
Could be a knackered Pump!
Someone mentioned I think that the temp diff across the boiler should be 20C. I thought in those days they were all 10 or 11? Can't see it in the MI.
Another possibility.
Page 4 Table 2.8 shows the available pump head for design temperature diffs of 17C and 20C.
Hmm, "OK"? People get used to things.
This fellah was producing hot water in a Halstead.
I realise this saga started in the winter, but now it's summer the incoming could be near 20 C.
If you were at the boiler, it would take so few minutes to eliminate many of these things
!
You are making an assumption.
See MI's, Page 4 Para 2.8. This show info for diffs of 17C and 20C; 11C is not even mentioned.
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