Trouble with single 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!