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

[DP]

Eventually decided to look at the post. Fluff, 10 out of 10 for sticking with it and trying to understand the problem.

My take would be as follows.

System worked at one time. Problem radiator was replaced thinking that radiator was the problem but new rad still acting up.

Boiler is not oversized- it is a combi boiler. It is oversized to heat water and excessive central heating power is just a bonus. So, it will be able to provide you with just acceptable flow of hot water but able to heat three identical houses. Since radiator heating does not require full boiler capacity, it can be 'powered down' to heat the radiators gently instead of zooming to full power and then shutting down and going to sleep to wake some minutes later to start the heating process. Car analogy would be full power to reach 70 on the motorway and then foot off the accelerator. Your boiler will be in cruise control mode maintaing heat output needed by the radiators..

Your boiler has worked correctly in 'cruise control' mode (modulated correctly) before I take it. If it has, I see no reason to tweak the boiler power but Hailshams load calculation suggest might be prudent to do this.

Earlier saw the flow and return temperaturs that were wild. Check the temperature on the two 22mm pipes under the boiler. I would expect a differential between 11 and 20 degrees C if system working correctly. This is a tough ask- are you able to get someone to check the same temperature differential exists on the pipes at the main heat exchanger? What I am getting at is, what if internal 'short circuit' to flow of water is not giving you suficient flow through the problem radiator.

Is the new radiator manufactured for installation of a vent and blank plug at the top or is the radiator manufactured with vent plug. Reason for asking is, if the plug can be removed, you could close both rad valve, remove one of the plugs and install a 15mm fitting and length of pipe/ hose to allow water to discharge safely for next instruction. Get someone to man the filling loop. Open one radiator valve fully and maintain system pressure at the boiler. At the hose end look at the outflow.

Now close the filling loop, close the open rad valve and open the other rad valve, open filling loop valve and see if flow from hose end is same as above. If unsure, collect water in bucket for say 10 seconds. You should now be able to confirm if water flowing into the radiator is the same as water flowing out of the radiator.

Looking at the picture you posted, seems to suggest you had a back boiler or a wallmounted Baxi boiler installed by FEP, but I could be wrong. You have access to the manifolds. Can you check the temperatures at the manifold on the 22mm pipes and also on the microbore (not too close to the manifold). Post your finding. Hailsham has already calculated pipe size to be correct.

My suspicion is the 22mm capnut and 22x8mm reducer set but let us not jump the gun.

Pump speed needs to stay as max as this power is required during hot water mode,

 

[Agile]

Danny, if you read the last eight pages you would see that they have already done the bucket test and it indicates good flow to each valve.

You dont seem to recognise the other problem of short cycling because the CH power is set at max.

Whats needed is to set it to minimum to prolong the firing time and to minimise the anti cycle time to reduce the boiler off time.

Tony

 

[D_Hailsham]

If it is possible to alter the parameters of the boiler as per agiles post than you would be advised to do so ??

Does not appear to be possible on the Alpha CB28X.

I opened the hot water tap to a trickle without starting the boiler up. Then switched the boiler on for CH ...

Did the water out of the tap stay cold or did it get warm?

The test results are very strange.

Did you let the system cool down completely before all three tests (tap on, tap off, tap on)? If not, we cannot make a valid comparison between the results.

Did you get any unusual patterns on the red and yellow lights?

Assuming the first test was from cold we can deduce the following from the results:

1st time boiler fired for 19.30 minutes - heating from cold to 80C.
Boiler off for 3 minutes - time to cool down to re-light temperature
2nd time boiler fired for 5.30 minutes - time from re-light temp to 80C
Boiler off for 3 minutes - time to cool down to re-light temperature
3rd time boiler fired for 5.24 minutes - time from re-light temp to 80C
Boiler off for 3 minutes - time to cool down to re-light temperature
4th time boiler fired for 5.11 minutes - time from re-light temp to 80C

Once the boiler has reached temperature from cold it is running on a five minute on, three minute off cycle. It is doing this because it needs to be below the limit of modulation. The three minutes off is preset on the boiler; the pump runs during this time to cool the boiler down. When the boiler relights it automatically goes to max power and reduces it if necessary.

 

[fluff29]

Agile, I saw your post on the settings. Am i right that I would need an engineer to do this? If so, what do I need to ask them to do? When I explain what has been happening, they will tell me that I don't need to change the settings and I will get the old lines of it needing a powerflush, piping wrong, new boiler needed, etc. It is a never ending circle, they all want to try their own thing and they do not listen to what I have already done.

D_Hailsham,

With the water on a trickle, and the CH on, the water got a little warm but not boiling like it would when the hot water is turned on.

With regards to the test results. I never at any point allowed the boiler to start from cold other than at the beginning when it ran from cold for 19.30 minutes. I went from one test to the next immediately including when I turned the tap off and then back on again. I didn't turn the tap off or on mid cycle, it did it after boiler turned off.

Lights functioned as normal on boiler. Ie yellow light came on fully when burning and flashed normally when it clicked off.

The only way to do the 2nd part of the test again would be to fire the boiler up from cold tonight with the tap closed and time how long the boiler stays on for. I really can't see it staying on for 19 minutes the first time it is switched on, this has never happened before. Unless something has been magically fixed.

Do you not think that the diverted valve or what ever is controlling the diverter valve is the problem? Why would the boiler stay fired only when the hot tap is open a little if it wasn't a boiler problem. Can't be the piping as water is circulating.

Hope this explains things abit better.

Fluff

ie from 1st to 4th time

 

[D_Hailsham]

Agile, I saw your post on the settings. Am i right that I would need an engineer to do this?

Did you see my earlier post? The Alpha CB28X cannot be adjusted in the way Agile suggests.

With the water on a trickle, and the CH on, the water got a little warm but not boiling like it would when the hot water is turned on.

So the diverter valve could be opening slightly to allow the water through the HW heat exchanger. This could account for the tap water warming up.

I never at any point allowed the boiler to start from cold other than at the beginning when it ran from cold for 19.30 minutes. I went from one test to the next immediately including when I turned the tap off and then back on again. I didn't turn the tap off or on mid cycle, it did it after boiler turned off.

That's what I thought. In which case, I don't think the diverter valve has anything to do with the problem.

You say that you only turned the tap on and off when the boiler was not running and the tests went in sequence. I assume this means the tap was turned OFF in the three minutes the boiler was off, between test 4 (5.11) and test 5 (0.35); and the same between tests 7 and 8. So if you put all the results together, ignoring the three minutes OFF times, you get:

Tap ON with boiler cold
1. ON 19.30 minutes.
2. ON 5.30 minutes
3. ON 5.24 minutes
4. ON 5.11 minutes
Tap OFF during 3 min Boiler OFF
5. ON 0.35 minutes
6. ON 3.10 minutes
7. ON 3.05 minutes
Tap ON during boiler 3 min OFF
8. ON 9.50 minutes


No 1 is obvious - the boiler is heating up from cold. No's 2 to 4 are as I explained earlier; but it's interesting to note that the ON times are getting progressively shorter.

No 5 is an anomaly, which can't be explained by turning the tap OFF. Unless the boiler relit before it had time to cool down, so it only took 35 secs to reach the set temperature.

No's 6 and 7 - the ON time is getting progressively shorter.

No 8 is another anomaly. Unless some of the heat is getting diverted through the HW heat exchanger.

It would be instructive to do the test from cold first with the tap off and then with it on. You need to keep the boiler going for at least an hour each time, to see if the ON times eventually level out or get progressively smaller. I would suggest doing the two tests on consecutive days, so the system has time to cool right down.

 

[fluff29]

Hi all

Just had the wind taken out of me.

Spoke to Alpha technical (this guy seemed very knowledgeable).

He said there is nothing wrong with the diverter valve. He said that we were tricking the boiler into thinking that the DHW was on when we left the tap open a trickle.

He said that the rads were heating up but at a slower rate than what they should do as the heat from the boiler was not coming through at full power when we did this.

He said from the symptoms that we have a blockage and the water isn't getting away from the boiler quick enough. I did tell him about the bucket tests, etc but he still thinks there is a partial blockage somewhere (either sludge or debris).

What he did say was that we would be lucky to get anyone to powerflush microbore, yet this is what a few plumbers have recommended. He said that we could get leaks due to pressure on the small pipes. He suggested a cleanser instead.

D-Hailsam, now see we can't adjust our boiler. You are also spot on with your deductions on what we did with the boiler last night. The tap was either put on or off during the 3 mins that the boiler was off.

Are we back to a blockage again or an oversized boiler or a possible combination of both???

thank you all for your time and effort.

I greatly appreciate it.

fluff

 

[D_Hailsham]

Spoke to Alpha technical (this guy seemed very knowledgeable).

Presumably a different guy to the one you last spoke to!

He said there is nothing wrong with the diverter valve. He said that we were tricking the boiler into thinking that the DHW was on when we left the tap open a trickle.

I think he's spot on.

He said that the rads were heating up but at a slower rate than what they should do as the heat from the boiler was not coming through at full power when we did this.

Is he saying that, with the tap slightly open, the boiler is running at a lower output? If so, repeating the tests as I suggested should prove this.

He said from the symptoms that we have a blockage and the water isn't getting away from the boiler quick enough.

Possibly to the dining room rad, even though your bucket test seems to disprove this. Was he aware that you have only 12kW of rads?

What he did say was that we would be lucky to get anyone to powerflush microbore. ... He suggested a cleanser instead.

That's a good suggestion.

1. Drain the system and run cold water through until it runs clean.
2. Refill and add two cans of Sentinel X400 to the system and allow it to circulate for about four weeks.
3. Repeat 1
4. Refill and add a can of Sentinel X100
5. If you live in a hard water area, also add a can of Sentinel X200

If you want to do a really good job, you need to allow the water to circulate through one radiator at a time for about 30 minutes. You do this by closing all rad valves except the two on the rad being flushed, which should be wide open. Do the same when running the cold water through.
Set the Central Heating thermostat to minimum while the water is circulating.

Are we back to a blockage again or an oversized boiler or a possible combination of both???

blockage - possibly; oversized boiler - definitely.

A DIY clean is much cheaper than a new boiler; so try that first - after you have done the tap tests.

 

[vulcancontinental]

What he did say was that we would be lucky to get anyone to powerflush microbore, yet this is what a few plumbers have recommended. He said that we could get leaks due to pressure on the small pipes. He suggested a cleanser instead.


fluff

You've had good advice but I'd just say I think you would be unlucky to get people to flush microbore - it just isn't something the flushing machine manufacturers recommend as it isn't always successful.

Far more effective I find to flush gently over a long period as explained.

If you can bear the extra work take the rads off individually, attach a hose and flush them through outside one by one.

What a saga!

 

[DP]

Have cut and copied information found in 8 pages.

*Boiler - Flow F87.8 Return R43.7
*Kitchen - F79.3 R49.7
*Dining Rm - F81.9 R41.9
*Living Rm - F84.0 R50.3
*Bathroom - 80.3 R74.5
*Hall - F82.2 R49.1
*Daughters room - F80.7 R56.0
*My room - F79.7 R51.3

Tony wrote

Danny, if you read the last eight pages you would see that they have already done the bucket test and it indicates good flow to each valve.

If lack of circulation was not the main problem here, I would be expecting to see temperature differential seen at "My room" across other radiators as well. I might have missed flow and return temperature differentials when I 'speed read' the 8 page discussion.

1st time boiler fired for 19.30 minutes - heating from cold to 80C.

If in 20 minutes flow and return do not show 20 degree (more like 10 with lockshields wide open) differential, i think bucket test has been useless and the bucket should be kicked into the rubbish bin

The rad sizes add up to approx 13kW

Hailsham has calculated the heat load to be 13kw- boiler will modulate down to 11.2kw. Tony I thought you were an electronics man. As such you do not have much faith in electronics if you are suggesting the boiler will not 'cruise'control down to 11.2kw especially when the return temperature is average of 30 degree beklow flow temperature. Also, how do you modulate a boiler that cannot be modulated.

Copied from boiler MIs.
The burner is lit electronically and the heat output is controlled by a modulating gas valve.
The fan will run at full speed; once the air pressure switch is proved the burner will light. The burner output then automatically adjusts to suit the system demand; as the temperature of the water in the boiler approaches that set by the adjustable temperature selector, the burner output is reduced.

You dont seem to recognise the other problem of short cycling because the CH power is set at max.

Can you tell me how you would range rate this boiler and remain faithfull to Gas Safety (installation and Use) Regulations

Whats needed is to set it to minimum to prolong the firing time and to minimise the anti cycle time to reduce the boiler off time

Boiler off time is 3 minutes. How do you propose to reduce the 3 minute off time?

OP, could you check some of the bits I suggested in my earlier post? I suspect the diverter is passing to HWHE hence FULL pump power is not available at the rads. 28kw is available on tap, boiler cannot even heat 13kw load. I would want to look at the return pipe into the main heat exchanger to see if it showed almost nil temperature difference (which might be the reason why the burner is shutting down before the rads are up to temperature)

[/quote]

 

[joop1977]

Ignore the oversized boiler posts,absolute ******.

 

[D_Hailsham]

The rad sizes add up to approx 13kW

Hailsham has calculated the heat load to be 13kw- boiler will modulate down to 11.2kw.

But it's only 13kW in the depths of winter. Most of the time it will be less than 6kW.

Copied from boiler MIs.
The burner is lit electronically and the heat output is controlled by a modulating gas valve.
The fan will run at full speed; once the air pressure switch is proved the burner will light. The burner output then automatically adjusts to suit the system demand; as the temperature of the water in the boiler approaches that set by the adjustable temperature selector, the burner output is reduced.

You missed an important chunk out!

6.1 CENTRAL HEATING MODE
... the burner will light. The burner output then automatically adjusts to suit the system demand; as the temperature of the water in the boiler approaches that set by the adjustable temperature selector, the burner output is reduced. When the set temperature is reached, the burner is turned off.

I take that to mean that each time the boiler lights, it initially goes to max output and then reduces output as it near the set temperature.

Can you tell me how you would range rate this boiler and remain faithfull to Gas Safety (installation and Use) Regulations?

Boiler off time is 3 minutes. How do you propose to reduce the 3 minute off time?

It's already been established that these are not possible.

 

[fluff29]

Hi everyone

Never came on last night as I was depressed after talking to Alpha last night.

My boss phoned Alpha technical this morning. After he spoke to them, they have agreed that the diverter v/v assy should be stripped down, checked and replaced if necessary.

I therfore need to phone Homeserve tonight to log the call.

DP - I will not start doing any of your suggestions at the moment until I speak to Homeserve and see if they will send out the Alpha engineer rather than the local agents. I will try to get a hold of the temperature probe that I used before and check the pipes whilst I run the boiler with the tap slightly open and closed. I would also add, I do not know if the system has ever worked properly. I suspect the previous owner had probs as there is alot of fernox in the pipes and the owner had very high gas bills, over £100 per month as he had the open gas fire on in the living room all the time to supplement the heating. The person who fitted the boiler orginally came round to do some other work in my house last year when I moved in but after I contacted him to look at the boiler/system, he didn't return my calls and eventually he said he would not have the time to look at it, ever. Thought this strange at the time, but put it down to me contacting him in the winter when he had alot of good paying jobs on.

D-Hailsam, I will do the tests on running the boiler from cold over 2 nights with the tap slightly on and also off. This isn't too difficult and it will rule our out another thing if Homeserve replace the diverter valve and we are still having the same cycling problems. I haven't discussed the heat requirements, sizes of rads or modulating boiler with Alpha technical. I will need to do this next week if the v/v does not fix the problem.

Hopefully I am nearing the end of this mammoth post.

Thank you all for sticking with me through this stressful experience.

Fluff

 

[Agile]

I would be very surprised if there is not a range rating pot available even if its not mentioned in the MI.

Can any email an MI copy and ideally a copy of a picture of the PCB.

The anticycle time is often not settable on older boilers.

One problem on this is the rad never gets fully up to temp because for nearly half the time its on the off cycle.

Tony

 

[D_Hailsham]

D-Hailsham, I will do the tests on running the boiler from cold over 2 nights with the tap slightly on and also off. This isn't too difficult and it will rule our out another thing if Homeserve replace the diverter valve and we are still having the same cycling problems.

If you have the time, do the tests before Homeserve plays about with the diverter and afterwards. Then we can compare the results.

What temperature do you have the boiler set to for heating? Is it max or something lower?

 

[fluff29]

Hi

I will do the test tonight and tomorrow night.

It will be next week before homeserve come out anyway.

The heating is set at 7. This was the magic no for getting 70deg on the boiler.

fluff