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

[DP]

DH wrote

But that does not prove that the problem is due to poor flow through the rads.

DH, working on it. Awaiting further tests from Fluff. Story so far is flow through the HW HE is as one would expect. Further figures and data will be the acid test. All I can say is 'watch this space'. Either the fault will be loacalised or I will be learning a few things from this thread. Incidently, couple of years ago went to same boiler with very similar same fault. Did clear it. But in this case relying on data posted.

All I am saying just now is that boiler function as expected during hot water delivery, so fault has to be beyond the primary water flow as indicated in excellent picture posted by Chris (the boiler in hot water mode).

 

[fluff29]

Hi guys

Just tested water at the bath taps upstairs.

Cold water

10 secs = 18.1
20 secs = 16.4
30 secs = 15.3

Hot water

5 secs = 18.5
10 secs = 19.9
15 secs = 28.8
20 secs = 27.2
30 secs = 31.1
35 secs = 33.8
40 secs = 38.1
45 secs = 40.5
50 secs = 42.5
55 secs = 43.8
60 secs = 44.9
105 secs = 46.0
115 secs = 47.0
120 secs = 47.5
130 secs = 48.2
140 secs = 48.5
150 secs = 48.9

Hope this is enough details. If you need longer measurements on the cold, let me know.

Boiler set at no. 7 for DHW.

fluff

 

[fluff29]

Tamz

I don't think the balancing has too much relevance at the moment. Althought I balanced quite rigidly earlier in the year, since then I have been moving it around in the last couple of weeks as after the new pump was fitted a couple of the upstairs rads were not heating fully to the bottom. Opened the lockshield and it solved the prob.

However, I can give the system a run with everything fully open, just to test it. The problem rad is fully open anyway.

fluff

 

[Agile]

You seem to be missing the point!

To get even heating of the rads you dont want to upset the balancing.

The only thing you should consider is to CLOSE each lockshield on all but the problem rad a little.

Your 34°C flow/return differential indicates a serious flow problem.

The effect of that is made worse by the boiler short cycling.

Reducing the boiler power to lengthen the firing time will assist but the main problem is the restricted flow rate.

I expect that I have asked before but dont recall any answer, but what setting is your pump on?

Tony

 

[ChrisR]

but what setting is your pump on?

That was gone over - it's on full, being a combi.

I wonder if the boiler's modulating at all. I did ask Fluff to time the meter.....

 

[DP]

Fluff, pity you did not post the cold temperature readings at intervals. Your readings do show poor HW performance as at 30 seconds boiler has heated the water by 15 degrees only. At 150 seconds you recorded 49 degrees, a temperature rise of acceptable 34 degrees but what was the flowrate (water collection for 15 seconds)

Did a check on my boiler. It took all of 19 seconds to reach 49 degrees C.

Can you switch the power to boiler off, run the hot tap full open and collect water from the tap for 15 seconds. Let the water run until the temperature stabilises. Keep running the water and transfer the thermometer to what would be the hot water delivery pipe under the boiler. Switch the power on and start recording the temperature rise and time taken whilst keeping an eye on the 'A' light.

Was the A light solid throughout? How long did it take to get 35 degree C temperature rise? What was the quantity of water collected in 15 seconds? I would be looking for about 2.75l of water in 15 seconds.

The manifold seems to suggest an installation by FEP which usually comprised a Baxi wall mounted or a back boiler, single entry radvalves and cylinder that had an 8mm microbore return pipe to the manifold. Commonly there was no means of shutting off the rads in the summer other than manually turn the rads off at the valves. Finals at the manifold were prone to blockage on the flow where the 8mm terminated at the manifold. Also wonder if the gas line is correctly sized as nearly 3 minutes have elapsed to attain stated temperature rise but boiler could well be modulating and flowrate may well be below par and boiler set to 7 (is that full 'volume'?)

 

[D_Hailsham]

The manifold seems to suggest an installation by FEP which usually comprised a Baxi wall mounted or a back boiler, single entry radvalves and cylinder that had an 8mm microbore return pipe to the manifold. Commonly there was no means of shutting off the rads in the summer other than manually turn the rads off at the valves.

You are way of track here! The OP has an Alpha CB28X combi boiler.

One possible cause has crossed my mind. The OP said, very early on, that there are TRVs on all rads and that there was no bypass (the X version does not have a built in bypass). Could this have an effect? Also there does not appear to be a room thermostat.

Who or what is FEP??

 

[fluff29]

Morning all

Agile - the original pump was at max, reported this before when DH asked me to check it. There is now a new pump fitted by it has no indicator of where it is set other than the screw.

I orginally tried balancing system. Since then, I have had to open the 2x bedroom and hall rad a little. I would say this has de-restricted the flow that I orginally had, as originally every lockshield was turned back to the minimum necessary to heat the rad, starting at the closest rad to the boiler (or am I not understanding this fully).

DP- I have not done your tests correctly. Will run the cold water test again tonight.

Can you switch the power to boiler off, run the hot tap full open and collect water from the tap for 15 seconds. Let the water run until the temperature stabilises. Keep running the water and transfer the thermometer to what would be the hot water delivery pipe under the boiler. Switch the power on and start recording the temperature rise and time taken whilst keeping an eye on the 'A' light.

Does the above mean that the power to the boiler should be turned off until I have collected 15 secs of water from hot tap (which will be cold water) and the cold water coming out the hot tap has stabilised and am I to do this from the bath tap again? Then you want me to check the temperature at the DHW pipe below the boiler?

Also, with regards to FEP, another plumber who came round said that it looked like an FEP manifold. There was a back boiler originally and then a small wall mounted boiler under the stairs, one of the old square metal things when looking from outside house. Alot of the houses have them, the house I live in was bought from Wimpey by the Prison service and they installed the heating, double glazing, etc in mass for the wardens, hence every house has the same boiler unless they have replaced, like ours.

Haven't checked the gas rate that ChrisR spoke about, will do that tonight as well. I think the boiler goes up to 9 on both heating and DHW, and I have both set at 7.

Not sure if you can see the pump from the picture I posted on sunday. You may be able to tell me if it is on full.

fluff

 

[D_Hailsham]

Not sure if you can see the pump from the picture I posted on sunday. You may be able to tell me if it is on full.

The speed adjuster switch is on the top of the pump. It seems to be in the max speed position, but you may be able to check with a small mirror. The speeds are marked: |, ||, |||. It needs to be in the ||| position.

 

[Agile]

You need to measure the gas at maximum AND at mimimum as I requested so that we can know that the boiler is able to modulate properly.

Any hot water measurement is meaningless unless the hot water flow rate is set at the tap to about 11 litres per minute.

Tony

 

[fluff29]

Had to resort to a snickers to read posts. My head is nipping.

right, checking the gas.

I think I have an old meter.

1. Do I check for one revolution and time it as it says in ChrisR's FAQ? This will show me the length of time it takes to burn gas or do I do it for 15 mins.

2. Do I do it with the heating on or hot water?

3. Do I need to check how quickly it goes around when it is on high flame and also on low flame?

4. How do I know if it goes to low flame? When I have looked through the hole, I think the flame has always stayed the same, but I could be wrong as I wasn't paying too much attention. Is it noticeable from low to high flame?

Any help on this would be appreciated.

DH - I think FEP were a company in Scotland who fitted quick/cheap CH in the 80's, not 100% sure. And yes, I do not have a by-pass or any rads without TRV's. My boss and one point thought that if there had been, it could have been short circuiting around the by-pass.

fluff

 

[Agile]

You time in seconds for a full turn of the meter dial and write it down.

You need to do it on high flame and on minumum.

I explained how to get the boiler to do that about 2-3 pages ago.

The flame is meant to change its size but that test above will confirm this and give us the power input in each case to enable us to see if the boiler is working properly.

Tony

 

[fluff29]

Agile wrote

He needs to do that at full power with temperature at max and a hot tap on full flow.

More relevant to this problem is the second part with the temp turned down to minimum and flow at tap at about 25%. The flow rate may need to be adjusted slightly to be the lowest at which the burner stays on.

Agile, is this what you referring to on page 10? Is this to check if boiler is modulating. Sorry this is the only info from yourself that I can see which maybe relates?

Am I just putting DHW to maximum and putting hot tap on full at bath?

Fluff

 

[Agile]

Thats it.

We need the full power gas rate AND the minimum power gas rate.

Thats to check the power settings are correct and that its modulating.

Tony

 

[kevplumb]

yer going for the record on this one fellas

keep plugging yawll will get there