Trouble with single pipe system

[Single pipe Sean]

Hi Everyone, I’m new to this site so not quite sure how it all works or if this is even in the right place but here goes.

I live in a large property that used to be one of the training centers for Lucas Engineering. However it has since been converted back to a residential dwelling.
The house has a single pipe system with very large pipe work and 42, 4 column cast iron ideal radiators. We used to have an old ideal floor mount boiler (I think 70kw). We have since upgraded it to a vailliant ecotec 64kw and made it a pressurized system along with a 80l expansion vessel.
We are having problems maintaining the right pressure.
When the heating is off the boiler reads 1bar, the second it turns on and the big external pump kicks in it jumps to 1.5bar and stays there. When left at this the majority of the radiators work fine but around 8 or 10 don’t come on until the pressure is increased to around 1.8bar at the boiler. And we seem to have to top this up most days. The plumbers who installed the new boiler just don’t want to know and won’t come back, we’ve had a couple other people out but no one seems to know much about this type of system.
There seems to be no sign of leaks as most of the pipe work is surface mounted.
Could the expansion vessel pressure need to be increased?
Any advice would be greatly appreciated.
Thank you.

 

[Chuck]

When the heating is off the boiler reads 1bar, the second it turns on and the big external pump kicks in it jumps to 1.5bar and stays there. When left at this the majority of the radiators work fine but around 8 or 10 don’t come on until the pressure is increased to around 1.8bar at the boiler.

If you need to top it up daily, it's leaking somewhere you just haven't found where yet.

I'll be surprised if a heating engineer used to 'commercial' systems would have much difficulty sorting you out. Domestic installers are allowed to go up to 70kW but most of their experience will be with systems that are rather smaller. If you used the latter for the work you may find switching to another firm who domore of this sort of work is the easiest solution.

Anyway, to get the ball rolling, can you provide a diagram showing where the various components and pumps are located with respect to each other, please? Also a few photographs of the installation are always helpful.

 

[SJB060685]

@John.g do I remember you saying about the cgarge of a vessel being able to boost the pressure of circulated water slightly if increased? You're pretty good at this and I have no practical experience with commercial systems.

 

[Single pipe Sean]

Hi guys,
Thank you for your replies. As for topping the system up I only do it every night to get the remaining few radiators hot, however if I don’t top up the pressure won’t go any lower so I’m not sure about leaks.
I was looking into expansion vessel sizing and I’m not sure if I’ve worked it out correctly. The boiler says there is 5200 lites of water per min in circulation, is 80l big enough? The boiler is located in the cellar and the house is three storeys with a large 4 inch heating pipe going all the way up into the loft so I would say there’s around 12m of head.
I will attach some photos for you to see.
Thanks again.

 

[ShaunCorbs]

Sounds like the expansion vessel is slightly low on pre charge / not charged to system pressure

 

[Last Plumber]

Obviously I have not seen the system you have but if the main heating pump can effect the boilers, you need to separate things, either with a header of some sort or a plate heat exchanger. The external pump will only cause problems if it isn't already.
The loss of pressure is a leak or loss via other means but needs finding.
Vessel (rough wild guess) 200 gal system? Haven't seen it but I am imagining a building the size of approx 8 typical 3-4 bed family homes if that helps you any?

First job, header or plate in my opinion.

 

[SJB060685]

The expansion vessel is sized based on system volume and the temperatures the system reached. If you go into real detail then one would use minimum system pressure, maximum system pressure etc etc as well.

 

[Single pipe Sean]

Obviously I have not seen the system you have but if the main heating pump can effect the boilers, you need to separate things, either with a header of some sort or a plate heat exchanger. The external pump will only cause problems if it isn't already.
The loss of pressure is a leak or loss via other means but needs finding.
Vessel (rough wild guess) 200 gal system? Haven't seen it but I am imagining a building the size of approx 8 typical 3-4 bed family homes if that helps you any?

First job, header or plate in my opinion.

Thank you for your reply.
It’s a large 10 bedroom house.
42 of the big 4 column radiators that weigh a tonne!
A header plate was installed to start off with but the plumbers uninstalled it as the heating wasn’t working at all. But I think back then they were too scared to increase the pressure to anything above 1 bar with it being such an old one pipe system.

 

[exedon2]

Hi was it sealed system before new boiler fitted? Still got original rad valves? Any auto air valves?
Should be possible to calculate system volume i suspect with the amount of 4in pipework you appear to have 80lts is probably pushing it a bit.

 

[Single pipe Sean]

Hi was it sealed system before new boiler fitted? Still got original rad valves? Any auto air valves?
Should be possible to calculate system volume i suspect with the amount of 4in pipework you appear to have 80lts is probably pushing it a bit.

Hi it was an open vented system before and worked perfectly until changed to a pressurized system. All radiator valves are original but no signs of leaks from any of them. As for the auto air valves one was installed at the highest point in loft.
Thanks

 

[EvilDrPorkChop]

Am I missing something, where's the low loss header?

Also personally for me, that expansion isn't big enough for that system. On the face of it, 42 Cast Rads, 4 column that current expansion isn't enough. Got to remember there's non in the boiler either on them Vaillants.

 

[cr0ft]

My thoughts on this are that the expansion vessel probably isn't the culprit here. If the expansion vessel was too small you'd expect to see a very significant pressure spike as the system warms up. Unless I've missed it, you don't say you are getting a pressure increase as the system is warming up, rather instantly when the pump comes on.

If the pressure is jumping by 0.5 bar as soon as the pump comes on then all this means is that the pressure gauge is probably just after the pump. The additional pressure is the head of pressure being generated after the outlet of the pump.

You say you are having to top the water up in the system. You have a leak somewhere and this needs to be found.

If the radiators haven't been properly balanced then this needs doing in order to get them all warming up. It's quite possible a system of this size will need a low loss header as well which means you will also need primary and secondary heating pumps, i.e. one for the boiler and one for the radiator circuit.

As others have said, you really need someone with commercial design experience to make sure this all works properly, even though it's a 'domestic' sized boiler, it's certainly not a typical domestic system!

 

[Last Plumber]

Hi it was an open vented system before and worked perfectly until changed to a pressurized system. All radiator valves are original but no signs of leaks from any of them. As for the auto air valves one was installed at the highest point in loft.
Thanks

If you removed the header from that set up, I wouldn't expect it to work at all with that boiler. It probably wouldn't fire.
If it did, it would be nothing but luck or timing.

The vessel can be ignored for the time being. I think it may be fine but it isn't causing your current issue anyway.

Do you know the age of the system? If it is old enough to be installed without a pump (originally) then altering the pipe work in the loft (or anywhere else for that matter) could have a detrimental effect.

Why did you change to sealed?

As someone above said, you really need an experienced (possibly older too) commercial heating engineer to look it over. It will be worth paying for their knowledge.

 

[Single pipe Sean]

If you removed the header from that set up, I wouldn't expect it to work at all with that boiler. It probably wouldn't fire.
If it did, it would be nothing but luck or timing.

The vessel can be ignored for the time being. I think it may be fine but it isn't causing your current issue anyway.

Do you know the age of the system? If it is old enough to be installed without a pump (originally) then altering the pipe work in the loft (or anywhere else for that matter) could have a detrimental effect.

Why did you change to sealed?

As someone above said, you really need an experienced (possibly older too) commercial heating engineer to look it over. It will be worth paying for their knowledge.

In general the heating does work great, every radiator gets hot. I know usually with a single pipe system the radiators get cooler the further away they are but this isn’t the case. I believe the large flow pipe goes all the way up into the loft and works it’s way down through the house as radiators upstairs warm up first.
I’d say the system is about 60 years old maybe a bit older, its always had a pump fitted in the same place on the return side. No pipe work has been altered apart from the header tank being blanked off in the loft.
As for converting to sealed system, with old set up the gas bills were through the roof, and the old open flued boiler was apparently unsafe.
I will attach some photos of previous boiler.
Thank you.

 

[Last Plumber]

You have a concord and a Hideaway there by the looks of them. There are also three pumps. I suspect one for the cylinder. Why two Boilers and two pumps? Did you have two separate systems before all the alterations? Was the hideaway for the DHW cylinder and the concord running two heating zones?

I do think you'd be better with an experienced person with eyes on the job giving you advice. If 8-10 rads don't work unless you increase water pressure, something is obviously wrong. There is a good chance that whatever is leaking (if it is a leak from the old side) was leaking before the alteration. It would have gone unnoticed because of the F&E tank topping it up.

In a case like this one, I would have left the existing system be and installed a plate heat exchanger to completely separate the old world and the new. The existing system would then have run as before but be heated by a more efficient boiler.

 

[Single pipe Sean]

You have a concord and a Hideaway there by the looks of them. There are also three pumps. I suspect one for the cylinder. Why two Boilers and two pumps? Did you have two separate systems before all the alterations? Was the hideaway for the DHW cylinder and the concord running two heating zones?

I do think you'd be better with an experienced person with eyes on the job giving you advice. If 8-10 rads don't work unless you increase water pressure, something is obviously wrong. There is a good chance that whatever is leaking (if it is a leak from the old side) was leaking before the alteration. It would have gone unnoticed because of the F&E tank topping it up.

In a case like this one, I would have left the existing system be and installed a plate heat exchanger to completely separate the old world and the new. The existing system would then have run as before but be heated by a more efficient boiler.

Thank you for your reply.
Yes the one pump was for the DHW which has been out of action for over 10 years now. Also the other pump was for a separate circuit in an outbuilding which was also disconnect a while back. So it’s just the big pump and the internal boiler pump for the house system as it’s not zoned or anything. Not the best I know but don’t want to gut the house and convert to a 2 pipe!

 

[John.g]

(Replying to SJB, post #3)

Its recommended that you pump away from the expansion vessel, if the E.vessel is installed as close to the pump (suction) as possible then the pump will run with a head of E.vessel press+pump press so if pump (differential ) head is 0.5bar and E.vessel is 1.0 bar, outlet side of the pump will run at 1.5 bar, if installed on the discharge side of the pump then the pump discharge will be 1 bar and the suction 0.5 bar which even though unlikely can lead to air ingress if high system head losses and perhaps circulation issues.
This pump is running at 1.0 bar stopped and 1.5 bar running so E.vessel may be installed as recommended. Its interesting that all the rads heat up at 1.8 bar. Also very important with any system is the E.vessel pre charge and filling pressure, the filling pressure should always be higher than the pre charge pressure to give a little reserve so that the cold pressure is always at the required pressure.

Regarding the installed 80 litre E.vessel, if one assumes a average hot system temperature of 70C then a pre charge pressure of 1.0 bar with a filling pressure of 1.5 bar will result in a reserve of 16 litres and a final pressure of 1.84 bar ASSUMING the total system volume is 350 litres (I worked backwards), if the pre pressure is increased to 1.8 bar ( to get all rads circulating) then a filling pressure of 2.0 bar will give a reserve of 5.3 litres and a final pressure of 2.31 bar for the same 350 litres.

One way or the other IMO its vital to check those pre charge and filling pressures.

 

[Single pipe Sean]

(Replying to SJB, post #3)

Its recommended that you pump away from the expansion vessel, if the E.vessel is installed as close to the pump (suction) as possible then the pump will run with a head of E.vessel press+pump press so if pump (differential ) head is 0.5bar and E.vessel is 1.0 bar, outlet side of the pump will run at 1.5 bar, if installed on the discharge side of the pump then the pump discharge will be 1 bar and the suction 0.5 bar which even though unlikely can lead to air ingress if high system head losses and perhaps circulation issues.
This pump is running at 1.0 bar stopped and 1.5 bar running so E.vessel may be installed as recommended. Its interesting that all the rads heat up at 1.8 bar. Also very important with any system is the E.vessel pre charge and filling pressure, the filling pressure should always be higher than the pre charge pressure to give a little reserve so that the cold pressure is always at the required pressure.

Regarding the installed 80 litre E.vessel, if one assumes a average hot system temperature of 70C then a pre charge pressure of 1.0 bar with a filling pressure of 1.5 bar will result in a reserve of 16 litres and a final pressure of 1.84 bar ASSUMING the total system volume is 350 litres (I worked backwards), if the pre pressure is increased to 1.8 bar ( to get all rads circulating) then a filling pressure of 2.0 bar will give a reserve of 5.3 litres and a final pressure of 2.31 bar for the same 350 litres.

One way or the other IMO its vital to check those pre charge and filling pressures.

Yes that is interesting. I would say the total volume would be a fair bit higher and more like 600/700l judging by the size of the rads and length of pipe work.

 

[John.g]

OK then, why don't you increase the E.vessel pressure?, if I've interpreted you correctly you said that 1.8 bar is satisfactory.

A 650 lire system with a 80 litre E.vessel and 70C system temp should give the following:
Pre pressure Filling Pressure Final pressure reserve
1.0bar 1.0bar 1.43bar 0 litres
1.0bar 1.5bar 2.21bar 16 litres
1.8bar 2.0bar 2.70bar 5.3litres

 

[Single pipe Sean]

OK then, why don't you increase the E.vessel pressure?, if I've interpreted you correctly you said that 1.8 bar is satisfactory.

A 650 lire system with a 80 litre E.vessel and 70C system temp should give the following:
Pre pressure Filling Pressure Final pressure reserve
1.0bar 1.0bar 1.43bar 0 litres
1.0bar 1.5bar 2.21bar 16 litres
1.8bar 2.0bar 2.70bar 5.3litres

Yes I shall try that. As if left untouched the boiler will just stay at 1 bar and won’t drop below which is why I’m still doubtful there’s a leak.
Thank you

 

[cr0ft]

It’s very common to have leaks that only happen when above a certain pressure level.

 

[Single pipe Sean]

Hi Guys,
For those of you who are still interested.
Pressure in the expansion vessel has been increased and everything seems to be working perfectly for the last few days, no topping up! Not sure if this has solved it I shall keep an eye on it over the weekend!
Thanks again for all your advice.

 

[John.g]

What is the pressure cold and then hot, if you don't mind?

 

[Single pipe Sean]

What is the pressure cold and then hot, if you don't mind?

1 bar cold and 1.7bar hot (70degrees) which seems to be doing the trick fingers crossed.

 

[John.g]

Thanks, just trying to get a feel for your system contents, based on that and assuming a 70/60C flow/return temp.
The 80 litre E.vessel with a pre charge pressure of 0.5 bar and a filling pressure of 1.0 bar (reserve of 20 litres) with a final pressure of 1.7 bar would mean a system contents of 850 litres. A pre charge pressure is 1.0 bar (no reserve) would mean a system contents of 1125 Litres.