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!