Return pipe is not hot on radiators and pipe into boiler

[Yogeebare]

Hi
we have a Worcester greenstar 24i boiler (fitted for a number of years that was in the property when we bought it). We had an issue where the radiators were not getting hot throughout the home when we moved in and after tracing the pipework identified that the flow and return pipes were crossed in a couple of locations so we switched the TRV and lockshields on each of the affected radiators and this improved the situation.
However we have since had an extension and as a result have added some extra radiators - this was done by ourselves. The problem we now have is that only some of the radiators are getting hot and although the flow pipe into some of them is piping hot, the radiator stays cold and the flow pipe is cold too.
We also found out today that the boiler is not cutting off when the heating is on, meaning our gas bill will be huge
I have attached an image within my album which shows the layout of the home with the flow and return pipes marked and indicated where the pipes drop to feed radiators below.

As it stands currently the following radiators are getting heat at a temp we are happy with
1,2,3,4,5,12
the following radiators are getting some heat but not what we are happy with
6,8,10,11
the following are not getting any heat
7,9

however this is where it gets worse as radiator 7 will; after the heating has been on for a while; suddenly spring into life and 9 has heat at the flow pipe on the TRV but the return is stone cold.

Radiator 12 is heating up (even though it is last on the flow) and the return is red hot by the lock shield but despite it only then travelling approx 7ft back to the boiler the return pipe is only warm to the touch.

We had a plumber call in today and he is baffled but has suggested we loop the flow pipe to the return by the boiler to ensure this flows correctly (ruling out an issue with the boiler) and then if this is ok he would recommend replacing the pipework

I would appreciate any advice as we simply cannot afford to run the boiler constantly, and likewise we cannot have no heating. I have been round and balanced the radiators upto and including 6, and have also restricted the return on 12, but is the current run of pipes set up correctly, as I can not find clear diagrams / guides on this topic and I am wondering if the way the flow is set up is causing an issue

 

[D_Hailsham]

Looking at your diagram, the system seems to have been plumbed in a 'reverse return' configuration (also called a Tichelmann system).

View media item 1210
The return pipe travels the opposite way round to the flow which means that the pressure drop across each rad is almost identical as the total pipe length (flow + return) is nearly same for all rads. This makes balancing much easier.

Are there air bleed valves at the top of each vertical drop?

Check how far open the lockshield valve is on each radiator.

 

[Yogeebare]

Thanks for the response. I hope from my original post it was clear that I am not a plumber by trade so after some googling of Tichelmann system I am still unclear on;
1- is this a bad thing (they seem to imply that they cost more to run this way so is this why the boiler never seems to shut off?)
2- Is this setup compatible with all boilers (i.e should it work with the Greenstar 24i junior I have) or should I run a return from radiator 1 and cap the return from radiator 12?

In answer to your questions
1- No there are no bleed valves where the pipes drop through the floor, just elbows / tee joints - do they need a bleed valve or would it just make getting air out of the verticals easier?
2-As I had started to balance the radiators the lock shields are currently open fully on 7,8,9,10,11 as the heat was not enough to get a balance
the rest are open differing amounts as listed
1 is 1/4 turn open
2 is 1/4 turn open
3 is 1/4 turn open
4 is 2/4 turn open
5 is 1 1/4 turn open
6 is 3/4 turn open
and as 12 was getting so much heat this is now only open 1/4 turn. Do modern systems still require the 1st radiator to be fully open on both the flow and return as currently all have TRVs and as shown above the first is locked almost all the way on the return?

I have turned off all radiators today on the trvs and opened just one at a time. In doing so each radiator heats up very quickly and the boiler is switching on and off, so in my (admittedly uneducated view) the pipe works does not appear to have any blockages but I am happy to concede this may not be the case.

As the return pipe goes from the ground up into boiler is it possible there is something as simple as an air lock on this leg of the pipe and if so can this be bled at the boiler or would this require a gas safe registered plumber?

 

[D_Hailsham]

Is yours a combi boiler (instant hot water - no HW cylinder)?

1- is this a bad thing (they seem to imply that they cost more to run this way so is this why the boiler never seems to shut off?)
2- Is this setup compatible with all boilers (i.e should it work with the Greenstar 24i junior I have) or should I run a return from radiator 1 and cap the return from radiator 12?

1. The only thing against a reverse return is that it may cost more to install as you have to run the return pipe from the last rad back to the boiler. In your case this is not true as the run from rad 12 to boiler is actually shorter than from the boiler to rad 1. (PS There should be a blue dot in the top RH corner of the first floor with a blue connection to rad 2.)

2. Yes it's compatible with your boiler; and with any boiler.

1- No there are no bleed valves where the pipes drop through the floor, just elbows / tee joints - do they need a bleed valve or would it just make getting air out of the verticals easier?

...

As the return pipe goes from the ground up into boiler is it possible there is something as simple as an air lock on this leg of the pipe and if so can this be bled at the boiler or would this require a gas safe registered plumber?

I did wonder if air was getting trapped in the drops. Bleeding the rads will only clear air from the rads, not the pipework.

If rads are getting hot, I doubt if there is air trapped in the return into the boiler.

As I had started to balance the radiators the lock shields are currently open fully on 7,8,9,10,11 as the heat was not enough to get a balance

7, 9 and 11 are on the ground floor and all fed by drops. Possible air lock. Setting the LS valve fully open won't solve anything. It might even be worth shutting them off and seeing what effect it has on 8 and 10

the rest are open differing amounts as listed

They all seem about correct. 1 1/2 turns is probably fully open. The remaining turn or more is ineffective.

Do modern systems still require the 1st radiator to be fully open on both the flow and return as currently all have TRVs and as shown above the first is locked almost all the way on the return?

Do you have a room thermostat? If so there should not be a TRV on the rad in the same room.

I have turned off all radiators today on the trvs and opened just one at a time. In doing so each radiator heats up very quickly and the boiler is switching on and off, so in my (admittedly uneducated view) the pipe works does not appear to have any blockages but I am happy to concede this may not be the case.

If that is the case, it certainly suggests no blockages and no air locks in any of the pipes.

 

[Yogeebare]

Sorry, yes the boiler is a combi and we have no issue with hot water and I have amended image to show the return drop.
With no bleed valves in the drops is there any way to test for / remove air in these pipes? I am happy to drain the system and refill (again) but steps I have been taking so far when doing this are
- turn off all trvs and lockshields
- fill the system until approx 2 bar pressure
- starting at first ground floor rad I then open just the TRV and bleed till no air
- shut of TRV and move to next on flow (so I do 1,5,7,9,11,12)
- move to upstairs and repeat (so I do 2,3,4,6,8,10)
- then open all trvs and lockshields fully and turn on boiler
- go round and balance each in sequence
reading the boiler installation though it says to open both trv and lockshield on all rads and fill, then work way round and bleed???

I have shut off the TRVs on 7,9 and 11 but this does not appear to have made any difference to 8 or 10 and I find that now all are back on again the boiler seems to be running constantly again.

One other thing not mentioned yet is the pipework which for the best part is plastic (but is clipped pretty much all way round so no real dips I have seen) with some of the original pipes being copper.

All pipework though (with the exception of the first 8" or so is 15mm. Due to the volume of rads and sizes I have replaced the first leg of the flow from the boiler to the drop between rad 1 and 2 with 22mm but before I invest in replacing the rest (which means pulling up floors) I want to rule out everything else.

The bits I dont understand are
- rad 12 is the last on the flow, yet despite previous rads being cooler, this one gets to temp (is this because it is the smallest rad and water takes the easiest route???)
- the return pipe at rad 12 is hot but is no where near the same temp by the time it makes the short journey back to the boiler

just so everything is disclosed I have also added the dimensions of each rad on the image in case this helps identify the issue....

 

[D_Hailsham]

Thanks for the extra info. I will take it on board and think about the problem.

Are you using thermometers to balance the rads? If not, what system are you using?

 

[D_Hailsham]

I forgot to ask this: What is the GC number of your boiler? It should be on the cover of the Installation Manual.

 

[Yogeebare]

I really appreciate your efforts on this, but please if there are any other views out there do not be shy, I really am getting desperate now and the more collaborative we are the better - there has to be someone who has had the same experience.

I plan to drain system again in the morning and refill based on what Worcester recommend to do this but I really am pulling my hair out as I know it will be something blindingly simple that I have missed / cocked up and things like this keep you awake at night mulling them over.

After all the switching on / off today I re-bled radiators and got quite a lot of air out of 3 and 10 so maybe it is just an airlock

I used a digital thermometer but as I only have one I monitored to get the max temp on flow, then switched to return and monitored again.

I just re-read your previous response and to be clear the returns I listed are quarter turns, not 1 and a half etc for the first few on the run.

As for the GC number this is 24i junior GC NUMBER 47-311-86 according to the info I have

 

[D_Hailsham]

After all the switching on / off today I re-bled radiators and got quite a lot of air out of 3 and 10 so maybe it is just an airlock

The fact that you can get each radiator to heat up individually, means that there can't be an airlock.

Was the boiler turned off and allowed to cool down before bleeding the rads?

Which are the rads in the new extension?

What temperature drop were you trying to get across the rads?

I just re-read your previous response and to be clear the returns I listed are quarter turns, not 1 and a half etc for the first few on the run.

I had appreciated that. I was just pointing out that most LS valves are fully open at 1½ turns. The remaining turn or so, until the handle stops turning, does nothing.

Now that you have provided the radiator info, the valve openings do not appear to be consistent. I have used the Stelrad Elite catalogue to obtain the rad outputs and here they are, with LS valve opening:

1 - 2845W - ¼ turn
2 - 800W - ¼ turn
3 - 1000W - ¼ turn (towel rail estimated)
4 - 1400W - ½ turn
5 - 2254W - 1¼ turn
6 - 1142W - ¾ turn
7 - 1778W - Full
8 - 2489W - Full
9 - 1619W - Full
10 - 1778W - Full
11 - 2504W - Full
12 - 400W - ¼ turn

The first thing that struck me is that there is no relationship between the rad output and LS valve opening. There should be. Setting the drop across the rad determines the flow rate through the rad and, provided the drop is consistent, the flow rate is directly proportional to the rad output. i.e the flow through a 2kW rad will be twice that through a 1kW rad for the same temperature drop.

Assuming the flow though the LS valve increases proportionate to the number of turns open, we would expect the LS valve on a 2kW rad to be open twice as much as a 1KW. As rads 1 and 2 demonstrate, this is not the case.

Thanks for the GC number; it helped me identify exactly which boiler you have.

As for the boiler never turning off:

1. What controls (timers, thermostats) do you have?

2. What number is the temperature knob set to on the boiler?

 

[Gasguru]

Are you absolutely sure of the pipe layout?

Otherwise to me it looks as though it's just not balanced....some valves are open far too much. You haven't mentioned whether all the lockshields are of the same make. Some rad valve types are only a couple of turns fully closed to open, others might be 6 or 7 turns. When you have a mix it gets a real pain balancing.

Typically though I would say your towel rail should probably only be open an 1/8 of a turn or less. I suggest you shut this off for now and concentrate on balancing the rest, as towel rails being of just a few parallel pipes offer very little resistance and can have a dramatic effect on the system.

On another note the pipework is totally undersized at 15mm for a traditional 11 degree drop across the radiators so you may never achieve that when it's snowing outside. If the radiators are large enough they may provide sufficient heat (to heat the property) with a greater temperature drop of say 20 degrees.

 

[Yogeebare]

Hi,

Are you absolutely sure of the pipe layout?

As sure as I can be I have traced and retraced the pipes so many times I can draw them in my sleep.

You haven't mentioned whether all the lockshields are of the same make.

Again I cannot be sure on this having not fitted the originals, however none only require a couple of turns to open / close and I believe they bought from the same small supplier in the village.

I am resigned to the fact I may need to replace most of the 15mm with 22mm, but my priority is to get me through Christmas without doing this if at all possible. I fear that doing this may not cure the fault - but on the plus side it would mean I would be absolutely sure of the runs.

Was the boiler turned off and allowed to cool down before bleeding the rads?

It was turned off, but did not give it time to cool down ('')

Which are the rads in the new extension?

1,2,3,4,5

What temperature drop were you trying to get across the rads?

I was going for 12 degrees c but as you have already spotted there was significant variations as I worked round.

What controls (timers, thermostats) do you have?

I have the analogue clock with the dip switches to set the timer and we have no room thermostats, just the TRVs on each rad

What number is the temperature knob set to on the boiler?

Normally set to 3 (but the wife has a habit of cranking it up to 4/5 when she feels cold) but I have been testing on 3 and it was not shutting down

and now for an update on todays activity ..... I drained system and for return piping from 11-12-boiler I disconnected it where the drops are (as I needed to re-secure 11 to the wall) and I took the opportunity to blow down the pipes to ensure no blockages. There was some residual debris in the pipes (blackening around the joints and some fragments came out of the rad but nothing drastic.

I reconnected and refilled the system and set boiler to max / permanent and left running with all radiators open on both trv and lockshields.
Only the following got hot;
1,2,3,10,11,12
the following had some heat
6,8
the following were stone cold
4,5,7,9

Shutting off 1,2,3 has heated up 4 fully but 6 is still only warm and 7,9 are still stone cold so my question now is to balance, do I work round each rad in sequence (i.e 1,2,3,4,5 etc) or work on the order in which they get hot?

The only saving grace is the the main lounge is getting all the heat, but the bedrooms are suffering.[/quote]

 

[Gasguru]

I haven't read all the posts but do not set the cold pressure more than 1 Bar. Bin the thermometers for now, use your hands to measure the temperature drops across each radiator....they are more than sufficient to do the job.

Just to prove the pipe layout and get you started I suggest the following.

Set all TRVs fully open (and ideally remove the heads as sometimes TRVs fail and despite being set to max they can hold the pin fully/partially down).

Fully turn off the lockshields on radiator 2, 12 and rail 3 since these settings are absolutely critical.

Set lockshields on radiator 1, 8 and 11 fully open

Set lockshields on radiator 5, 7, 9 and 10 a 1/2 open

Set lockshields on radiator 4 and 6 a 1/4 open

Now turn on the heating. You should be running around the system constantly monitoring the temperature drops across each radiator. Leave 1, 8 and 11 fully open but if necessary adjust the others to get an equal drop.

Once these radiators are correct then you can sort out rads 2 and 12 and the rail. These will probably require an 1/8 of a turn or even less. Using a long screwdriver on the valve can tell you the point at which the valve opens. The rail in particular is likely to need a very low setting.

Once the system is hot it is difficult to set the balancing...it is best to wait till it cools and have another go.

Forget about the 11 degree drop, at this point you want an equal temperature drop across each rad/rail even if its 15 20 or 30 degrees. as mentioned before the pipe sizing is incorrect for the smaller temperature drops.

At this stage don't worry but TRV's should not be fitted to all the radiators....there should be one zone fitted with lockshields either end of the rad and that area should have a room thermostat.

 

[Yogeebare]

Hi
so..... after refilling the system and following the advice of Gasguru re the balancing and d_hailsham I was still having a problem getting heat around the house.

I then went back to basics and followed the pipe work into and out of each radiator again. This was as I believed correct, but I noticed that although the flow to radiator 4 was extremely hot, the return was cold and there was a significant area in the bottom quarter of the radiator by the return pipe that was still cold despite me opening the lockshield fully and turning off a couple of the previous TRVs on the flow.

I therefore took the radiator off and took it outside and flushed it out. There was not any discolouration or debris after numerous attempts (both flooding and also under pressure, and I turned the radiator a number of times and hit with a rubber mallet) so I also then opened the lockshield and let some of the water flow out of the return pipe.

When I replaced the radiator and filled it again (it is worth noting I filled slowly rather than opening the flow valve fully) and bled.
I then adjusted the lockshield again as per the advice, and touch wood, since then I now have heating around the whole house and the boiler is performing as expected

I hate issues like this as I have wasted many days trying to resolve and have paid for an engineer visit and numerous bottles of inhibitor, had advice from you both and I am sure that by following your advice it has played a part in resolving this issue, but hopefullly there will be something within this thread that will help anyone else suffering with a similar issue. It is just frustrating that there is no obvious reason as to what the issue was..

All that remains is to thank you for your help and guidance as there were many things I needed to do differently; like bleeding only when cold; so I am certainly a lot wiser

Wishing you a very Merry (warm) Christmas!!