Replacement radiator is colder at bottom than it is at top.

[ChrisR]

Poor Fluff - must be hard to follow everyone at once.
DP is making sense to me, not sure what Tony means, this morning!

Joop - can't see one - you have a look!
http://img821.imageshack.us/img821/6859/45215683.gif

 

[bluey831]

Fluff .... I have been following this thread - partly to learn and partly to understand better the problems with my own system. However, I'm losing the plot now so I can't imagine how it is for you.

If you have a Homeserve contract I would be onto to them pronto and 'insisting' they either fix it or provide solid written evidence that the boiler is not the source of the problem. You may be charged - however - depending how long you have been with them etc digging your heels in might minimise this.

Personally, I would then get at least two appropriately qualified specialists for an assessment and one of them to carry out the necessary work or to make recommendations for the necessary requirements to provide a fully functioning system. If it transpires that the fault was indeed related to the boiler then I would be writing a severe letter to Homeserve with a demand for money back and an amount for the inconvenience. If it is not related then you have a working system.

This thread and your problem has been active for nearly a year now and you are still stuck. Personally, I think these forums are excellent for the layman to get some good unbiased advice - accepting there will be differences of opinion between professionals. There is a danger of information overload and for the layman taking it too far - thus either invalidating any Homeserve warranty and/or making the problem worse and hence costing more in the long run.

I admire you patience for sticking with it - mine would have gone a long time ago. On the other hand, winter is fast approaching and having read all through the thread I'm hoping you and I will have working systems.

 

[D_Hailsham]

DH wrote

If it is acting as a short circuit, what would the effect be and why?

DHW HE would present a lower resistance loop, therefore less heat to rads.

Got that. I've just studied the pic posted by Chris R which makes it clear. If a hot tap is opened just enough to allow the diverter valve to open slightly, so some of the primary water passes through the HW hex, the HW hex effectively acts as another radiator.

What I did not realize is that, when a Hot tap is on full and the diverter right over, the two heat exchangers are in series, so heat still travels through both HW hex and CH hex. Presumably the HW hex is capable of absorbing all 28kW produced by the boiler, so the CH hex does nothing. However, if the diverter is only slightly open, the flow through the HW hex is much reduced, so the heat output of the HW hex will only be a few kW. Just enough to warm the tap water slightly, as the OP described earlier.

This raises the question: what does the OP's boss (and now Alpha tech) think is wrong with the diverter valve?

I can see the point of checking the pipe from HW hex to pump.

 

[fluff29]

I am running boiler for an hour with the tap off.

Flow pipe measuring 74.7 maximum whilst boiler running, return 41.5 just after boiler switches off.

Heat exchanger measuring 42.4 just after the boiler stops firing.

should the heat exchanger get this hot?

Hopefully chrisR is on to see this.

will continue running tests at the moment, but I don't see them changing much temperature wise. I will post results on completion.

thanks fluff

 

[Agile]

If those two temperatures co-existed at the same time you have a flow return differential of 33°C.

That indicates a very poor flow rate through the boiler/heating system and must have a cause. The pump could be one, either the impeller is blocked or the pump is weak and needs the finger test to check.

To DP and ChrisR, the gas rate tests at full power and at minimum power are to check if the boiler is set up correctly.

It can only modulate between maximum and minimum power as actually SET on the boiler and NOT as written in the book. Its a real boiler and before coming to any conclusion about modulation or power rating those settings have to be correct.

To DP, if it was my boiler at home and I wanted to reduce the minimum power to extend the modulation range then I would know what to do. But it would not be within the manufacturers operating parameters.

Tony

 

[fluff29]

Hi Tony

The flow temperature is taken with boiler running. The return temperature was taken just after the boiler switches off.

 

[DP]

Fluff, are you measuring the temperature on the pink pipe as 43 degrees?

 

[fluff29]

DP, yes, the pink pipe at the back of the pump going up the way which is the return, large pipe in red to the left of the pump is the flow.

 

[D_Hailsham]

will continue running tests at the moment, but I don't see them changing much temperature wise. I will post results on completion.

Fluff: I hope you are keeping a note of how long the boiler is on and how long it is off.

 

[fluff29]

yes, got my watch on timer and keeping a note of all times. Just finishing up and will post after I put the tatties on for the tea. Unhappy family - very hungry.

 

[fluff29]

The 2nd test that I did today have changed things slightly. Before the boiler only used to fire for 1 1/2 minutes. It fired for alot longer today. The only thing that we have done what I think would have made a difference in the last couple of weeks since it was cycling is the bucket test and a new pump fitted - although alpha agent said this did not help. Possibly dislodged a slight block??


Test no. 1 - boiler at no. 7
Hot tap open a trickle so it does not fire boiler
Times below are the length of time the boiler fired for.

Boiler if off for approximately 3 minutes between each time it fires.

The temperatures below were checked on the pipes below the boiler.

1st fire = 24.24mins - F72, R41
2nd fire = 5.52mins
3rd fire = 5.20 mins - F72, R40.8
4th fire = 5.44 mins - flow and return did not change much from the above.
5th fire 5.50 mins - R40.5

Pump runs for approx. 20 seconds, then there is still some other noise coming from the boiler, is it a fan. During the 3 mins that the boiler is switched off, it still feels like water is moving around the pipes, is this normal?

All rads heated up well and too the bottom, except the big prob rad.

Test no. 2 - boiler at no. 7
No taps switched on
Times below are the times that the boiler fired, boiler off for approx. 3 mins between times below.

The temperatures below were checked on the pipes above the pump.

1st fire = 16.26min
after 7 mins firing, F73.9, R27
after 14 mins firing, F74.9, R38.4
after 16mins firing, R40.5
when boiler switched off, R41.5

2nd fire = 3.10 mins
Checked heat exchanger after this cycle turned off, measured 42.2 degs. Checked it also during other cycles and it stayed around this temperature.

3rd fire = 3 mins
4th fire = 3.10 mins
5th fire = 3.02 mins
6th fire = 3.15 mins
7th fire = approx. 2.50 mins (during this time on I went around and turned all rads back to only 1/4 turn on for the lockshields as Tony suggested. From this point forward, the only lockshield fully open is the problem rad and it DID NOT help. The rad did not heat up any further at the bottom, it is slightly hot, just off the cold)
8th fire = 2.55 mins
9th fire = 2.55 mins

I used a hannah instruments K-thermocouple thermometer to check the temperatures. It has been calibrated.

Forgot to say when I did the first test and had the tap slightly open, the water got boiling hot after the boiler was firing for a while on CH.

I told Alpha what I told yourselves about the diverter valve & they didn't believe me. When my boss spoke to them, they believed them. Could he be coming from the point that the diverter should stay fully over for CH and if the hot water is put on a trickle, hot water should not come out the tap. Therefore the diverter must not be closing fully for the CH and therefore it is passing for the hot water. My own basic thoughts but possibly doesn't work like this.

Hope this proves something. thanks

 

[ChrisR]

40 something on the pink pipe - can you reach the pipe 130 I coloured red? isn't very hot - you'd get conduction anyway.
Is the return pipe from the heating hotter than 40 something? If so, my suggestion isn't the problem.

If the return's only 45 then the temperature sensor is suspect!
I though in your earlier posts the rteturns were hotter than that.


---

What I did not realize is that, when a Hot tap is on full and the diverter right over, the two heat exchangers are in series, so heat still travels through both HW hex and CH hex.

No they aren't in series, the diverter's like a changeover switch...

Have another look??

 

[fluff29]

Sorry chris, can't see pipe 130 (must be blind) I attached picture of my boiler. Where about is it? I checked the flow pipe (the big one to the left of the pump) and the return (pipe you can just see above the pump and towards the back of it). For the temperatures I did last night, I checked the pipes underneath the boiler.

NB: the boiler has been off for about 2 hours now. Do I need to run the boiler for a time before checking the 130 pipe again?

Also, for info the flow and return figures that I gave on 9 november (page 2) were done with the boiler at maximum. My recent tests were with the boiler at no. 7.

Also, a seal was renewed for leak we had earlier in the year, I can now see that the leak was from the pipe connected to the primary heat exchanger.

The pink pipe that you got be to check earlier, if this the return pipe for the CH as I thought it was and this is where I was taking my return temperature (did not check the temperature at the return pipe underneath boiler but I did use the flow and return pipes underneath boiler last night on the first test).

 

[fluff29]

DP - just reread you question earlier on re the temperature on the pink pipe. I was reading 41.5 on the pink pipe. It was the surface temperature on the heat exchanger which read 42.4. Sorry, trying to multi-task earlier on and didn't work.

Also, just re-read your post from last night. I have only checked temperature on the two pipes above, did not check them on the pipe below.

Do you want me to run the boiler again for another 20 mins and check them?

I would imagine they will be about the same as the pipes above (judging by my other test results of test 1).

 

[ChrisR]

Well it might be the rather dark one.... I suppose this doesn't help much...??