Any CH experts out there ?

[RogerS]

Can someone please confirm that I am correct in my thinking ?

The first photo is a rough drawing of how the CH layout used to work. The pump was located in the garage by the heat store. The pump fed a metre into the house where the feed split to two motorised valves. One valve sent the hot water down a dedicated pipe to the hot water cylinder. The second valve fed the CH feed and about another metre after this valve it split to feed the upstairs rads and downstairs rads. Within feet of where the split occurred, this feed pipe was hitting the radiators that it was designed to feed. Assuming that the system was reasonably balanced then my argument is that the temperature in this feed pipe is going to be roughly that when it left the heat store...give or take the odd degree.

NB the diagram does not show the CH split to the downstairs rads.

Now when my plumber put in the new boiler he was very fixated on neutral points and insisted that the pump be relocated up at the hot water tank and the feed and vent pipes connected there to create the neutral point. However this meant that the motorised valves needed to be located here as well which in turn necessitated modifications to the primary hot water feed.

The two original valves were removed and the T between HW and rads removed. The feed to the rads was cut off and blocked. The original and remaining feed to the HW tank became the main feed to the new pumps' location. Two new valves after the pump...the one we're interested in...the CH rad one then feeding a new pipe that T'd in part way down the upstairs original CH feed run.

With this new arrangement, I am 11 degrees of heat lower at the pump then that leaving the heat store because of the long run now built in to the system due to the new layout. 66 degrees leaving the heat store (don't worry about whether this is high enough etc for the purposes of this discussion) and 55 degrees when it hits the actual CH upstairs rad circuit. My plumber does not accept this. He says that I'd see the same thing on the original system which I think is bonkers. Original system...distance between heat store and first rad ...4m. New system...distance about 30m.

A pressurised system was and is out of the question as there was existing inaccessible pipework underneath the floorboards with joints of unknown provenance and as I'd already discovered one joint that wasn't properly soldered, I think this decision is sound.

Supplementary question. The furthest radiators from the CH feed point are in the kitchen. With every other radiator and HW tank off, the hottest temperature of the incoming CH water to these rads is a meagre 36 degrees. Is this an indication of an under-powered pump or a blockage in the old pipework ?

Second supplementary question. My plumber says that you get different temperature readings if the pipe is vertical or horizontal. EG horizontal copper pipe coming to a 90 degree feeding the vertical pipe into the radiator tail. Doesn't make sense to me.

 

[sunnybob]

As long as the pipes are inside the house, then it doesnt matter. the pipes are acting as radiators.

Here in Cyprus their Ch is bonkers. My boiler is on the garden wall, 10 feet from the house, with all pipes buried under stamped concrete so i have to heat up all that concrete before the house starts to feel the heat. The reason given is that so many houses blow up if the boiler is inside (there is no such thing as corgi here).
BUT, once inside the building, all the pipes are buried in the concrete floor and walls, right to the rad points.
The rads take a time to warm up, but the floor becomes very toasty and I can walk around barefoot on the tiles.
The kitchen floor will retain that heat for 24 hours after the Ch is turned off.

Either way, you are getting that heat into your building, either through the rads, or the pipes.

 

[RogerS]

As long as the pipes are inside the house, then it doesnt matter. the pipes are acting as radiators.

Here in Cyprus their Ch is bonkers. My boiler is on the garden wall, 10 feet from the house, with all pipes buried under stamped concrete so i have to heat up all that concrete before the house starts to feel the heat. The reason given is that so many houses blow up if the boiler is inside (there is no such thing as corgi here).
BUT, once inside the building, all the pipes are buried in the concrete floor and walls, right to the rad points.
The rads take a time to warm up, but the floor becomes very toasty and I can walk around barefoot on the tiles.
The kitchen floor will retain that heat for 24 hours after the Ch is turned off.

Either way, you are getting that heat into your building, either through the rads, or the pipes.

But that 'wasted' pipe is deep inside the core of the building and not really contributing. I know that the heat will leak out eventually but I;d rather it came out in the rooms where it is supposed to.

 

[Just4Fun]

Yes, all the heat will be going into the building somewhere, but there is little control over where. If the heat is dispersed by a radiator you can turn off that radiator if you wish. You can't turn off a pipe in the same way.

I would be concerned about the total temperature drop around the system. If I understand correctly, the flow out of the boiler is 66C and the return is something lower than the 36C going into the kitchen radiators, so over 30C temperature drop around the system. I thought a good target for temperature drop was 11C or 12C. I think 30+C is excessive.

 

[RogerS]

.....
I would be concerned about the total temperature drop around the system. If I understand correctly, the flow out of the boiler is 66C and the return is something lower than the 36C going into the kitchen radiators, so over 30C temperature drop around the system. I thought a good target for temperature drop was 11C or 12C. I think 30+C is excessive.

Not quite..the return isn't 36 degrees. That is the feed temp to the kitchen rads. I'm beginning to think that a section of feed pipe may be blocked ie that feeding the last two kitchen rads.

Plumbers are here at the moment. Found a lot of air in the system that normal bleeding wouldn't clear. We have yet to have the discussion regarding 'is there/isn't there a loss of heat and is it important' discussion

 

[Brandlin]

if your plumbers are finding airlocks that couldn't be bled from the rads, then that suggests uite poor installation allowing bends in the pipework to trap air. It's one of the things plumbers usually get very anal about as it can casue them A LOT of problems coming back to fix. It might point to some generally poor workmanship elsewhere too.

 

[RogerS]

if your plumbers are finding airlocks that couldn't be bled from the rads, then that suggests uite poor installation allowing bends in the pipework to trap air. It's one of the things plumbers usually get very anal about as it can casue them A LOT of problems coming back to fix. It might point to some generally poor workmanship elsewhere too.

This is an existing system that has had to be altered.


Update .....

OK....plumbers have spent 4 hours here and just left. Lots of air in the system and they spent a long time getting rid of it. Hoses, suction pump, the works. Some of that air was limiting the flow in the main return, we think. I could get one or two rads really toastie but fire them all up and they all became virtually cold which makes sense.

We've left the system to settle down for a few days and then he's coming back to do a final balance. Think that or two of those lousy Italian Cordivari radiators are Friday Night jobs. Time will tell.

We had the heat loss discussion. I came at it by describing a system where there was 500 yards of copper pipe between heat store and the first rad. Eventually he agreed with me. But we then had the further discussion about the discussions we'd had at the outset. There were the three options - as he reminded me.

Option A - keep the pump at the heat store and run two pipes down to it to create the neutral point. Trouble was that given all the steel etc in the building getting a clean run back - especially for the vent pipe that needed a gradual upward slope - was nigh on impossible.

Option B - the one we went for. Move the pump up to the area of the HW tank (where the feed and vent pipes were), make the tweaks to the circuit as outlined above. The option we went for. What I am a bit annoyed about is that he didn't point out to me the implications re heat loss in the changed circuit - especially as it was he who suggested the use of the heat store to run the boiler fully in condensing mode etc. This heat loss may mean that I can't run the boiler as efficiently as I wanted to and I've wasted all that money. Time will tell. He suggested that with the improved flow rate that it might not be as bad as it was. Fingers crossed.

Had I known about the heat loss then I guess I could have tried a bit harder to find a way to go the Option A route. Hard call. I do know that I tried damn hard the first time round (it was possible pump noise that was the driver as LOML has the hearing of a barn owl).

Option C - a pressurised system. Which, as previously mentioned, was ruled out due to unknown existing pipework provenance. We shall see...may have to bite the bullet and go for it downline.

Many thanks for all the advice, guys.

We have a toastie house

 

[NickN]

Would Option B (moving the pump) but feeding the radiators on the way TO the pump so that they got the full benefit of the heat have been an option? Although it would have reduced the hot water cylinder heat input, having said that, on the original design it looks as if the hot water cylinder feed had to run its way from the heat store to the tank, which must have been obviously a similar effect to what you're experiencing now, except that now it's the whole system losing that initial bit of heat.

 

[jimmy_s]

Whilst you will undoubtably be losing some heat due to the extended pipe run you would not expect to see that level of temperature drop.

I think you have a flow restriction due to a partial blockage or airlock. That would reduce the flowrate through the main cct causing the higher temperature drop.

 

[RogerS]

OK...we've moved on to a more thorny issue and the heat loss has been parked for the moment.

Over the last couple of weeks, there have been several times when the system has gradually ground to a halt insofar as any heat. A few upstairs but very lukewarm and nothing downstairs. A very cold house for several days. The plumber came back and removed the bleed valve on the upstairs rad furthest away from the pump and connected a hose pipe in its place, opened up the lockshield and nothing came out. He had to get his suction pump to get any sort of movement. After several hours the system was finally purged of air from the main pipes and all the rads started working.

Then a few days later I had to turn the pump off to do some electrical work and after switching it back on, the problem returned. After a lot of cursing I managed to get rid of the air once more.

OK...elsewhere another experienced plumber asked me to stick the end of the ventpipe into a bottle of water, turn the pump on and off and see what happened. The ventpipe is at the neutral point. Turn the pump off and the vent pipe bubbled into the water. Turn the pump back on and water was sucked up into the ventpipe. I am out of my depth now. Is this normal ?

 

[jimmy_s]

Roger the vent pipe is not at the neutral point - the cold feed connection is the neutral point. The vent pipe must be on the negative side of the neutral point as when the system is running the water level is dropping - when you stop the pump the water level equalises with the level in the F&E tank and displaces air - hence your bubbles. When you turn the pump on again the water level in the vent drops - causing water to be drawn in. It sounds normal.

If you want, PM me an I will try and give you a hand sort this out

 

[RogerS]

That's very kind of you, Jimmy. PM sent

 

[RogerS]

Just thought I'd give an update and a drawing of the system.

House ch layout

Where it says 'other rads' these are upstairs ones. Flow from heatstore is hidden by the heatstore return pipe.

The radiator marked 'bleed' rad is approximately in the right position and is the one (a) highest in the circuit and (b) furthest rad upstairs from the pump. My plumber called me up yesterday to see how things were going as he has a free day tomorrow. We agreed that I'd try switching off the pump to see what happened. Answer....an airlock when I started it up again.

I have a permanently connected drain cock in place of the bleed valve on the 'bleed' rad. So connect up a hose and open the lockshield. Some air bubbles and then nothing. No more air. No water. Remember the system has been working fine and that radiator was hot and so has water in it. So there's not enough head to push out any water/air in the pipes.. Unless ....unless :idea: you switch the pump off when you bleed, yes ? In that case doesn't the pump act as a block to the flow...which explains why nothing comes out ? But then surely the head in the tank is still acting to push the water out as it's acting back through the flow from the heat store, through the heat store and back up the return to that bleed rad...so it should vent. You have to stick suction on the end of the hose to get it flowing again,whereupon air and water comes out of the hose/lockshield route.

This time was also different in that when I closed the lockshield and opened the flow on the rad, I got a lot of air out. Very confusing

 

[Duncan A]

I'm no plumber, but have messed around with CH systems from time to time, and I've always understood that the radiators should be bled with the pump off so that the only pressure differences acting upon the system are those due to the head. My own experiences reinforce this understanding.
Newly filled systems come with air entrained in the fresh water, so you will get air apparently appearing from nowhere for some time.
Have you tried bleeding all of the radiators daily when the system is shut down? This may prevent a buildup of air causing an airlock.
Once the entrained air has gone, the system should settle down - if this turns out to be the problem and not something else of course.
Duncan

 

[RogerS]

Sorted ! :eusa-dance:

Plumber fitted a more powerful pump yesterday albeit much more expensive. Reasoning went that (a) we knew there was air in the system - from dissolved air in the fresh water being introduced when we hose-pipe bled but (b) the initial pump wasn't man enough to push the air out from wherever it had accumulated.

So...more powerful Grundfos pump and bingo...ran the pump at its highest speed and system worked just fine. Let it get back up to temperature and then switched it off for 30 minutes. Turned it back on and rads warmed up everywhere...upstairs and downstairs. This morning I turned it down to its lower speed and repeated the test. Again..all rads returned to normal working. No hose-pipe bleeding required.

There are also several unexpected bonuses.

1) Any air in the system either goes up the vent pipe or accumulates in the top of that radiator I was using to hose-bleed. A doddle to bleed the air out now.

2) Because it's running the water through faster, means that there is less time for that central main pipe to lose heat in an unwanted area. The rads seem hotter as a result.

3) Saturday morning woke to find the trip in the garage gone. Further inspection revealed that the old circulating pump we'd pressed into service for the boiler primary circuit had burnt out. The pump we took out from indoors has now replaced it ! Just got to take the new one I'd bought Saturday morning back to see if I can get a refund. Plumber called me while I was on my way back...too late to avoid the purchase.