Heating system problems, pro tips welcome.

[Rickf29]

Basically i've been called in by a friend of a friend to try and sort out their heating system that, it transpires, hasnt worked properly since it was adapted a couple of years ago.

100000 btu oil boiler is currently trying to feed 22 radiators and 3 cylinders with a grundfos 15/50 pump after a B&B section was added. I realise the boiler is the first problem and it doesnt cover the required heat output for the system but they simply dont have the money at the moment to change it.

The existing system was a 10 rad 1 x42x18 cylinder fed from 28mm pipe. This worked fine at the time. A plumber then came in and added 12 radiators from the 28 mm flow (before it is zoned) with no zone control. He ran 22mm's through an awkward loft space before increasing to 28mm again. Some of them work intermittently when the other system is calling for heat/hot water. After months of fiddling unsuccessfully they added en-suites to the B&B rooms so also coupled on to the unzoned 12 rad heating circuit is now 2 extra 36x18 cylinders also with no zone control.

What i'm after is a bit of advice on what to do. Personally I would create 4 zones from the system HW B&B HW Main part of bungalow CH B&B CH Main part of bungalow. The pump is inadequate for the system so what would my options be in the next size up of Grundfos, maybe a series 100? What type of bypass valve would it be best to fit once it is zoned properly and the bigger pump put in? I realise the problems with putting the system right without increasing BTUs of boiler but its a no go at the moment.

I only popped in quick on the way home today but I can get more information if its needed.

Thanks, Rick

 

[ALEC1]

can you get a decent performance from the heating with the cylinders shut down?

 

[Rickf29]

When the existing cylinder is satisfied the heating in the new part of the bungalow starts to filter through. However since adding the 2 new cylinders the time it takes is considerably longer. The old 10 rads always get up to temp quite quickly and it seems that when the TRVs start to shut down the volume of water forced down the new leg increases and manages to heat some of the 12 new ones (3 have never worked but i couldnt get to the pipework in the loft due to how much there is up there to make a proper diagnosis at the time)

The old plumber has had them working as independant systems so i'm told. He shut down the Cylinder stat on the old boiler and turned all the old 10 rads off, turned the heating on and where the water then circulates through the new unzoned bit after a couple of hours it was nearly at full temp. The problem this poses is that the heating temp is at about 75 degrees and with no stats/zone for the new cylinders it's a scald risk.

 

[ALEC1]

it sounds like the solution is to balance the heating system with the cylinders shut down, and the give some sort of hot water priority to the cylinders...

It could of course be that cylinders have small coils and take too long to heat up. Turning on the immersion heaters (if there are any will help)

Modern decent boilers have hot water priority meaning you can run the radiators at lower temperatures than the hot water...

 

[dcawkwell]

The boiler of 30kw is approximately ok for the heating requirement.
A bit short if including the hot water but that can be made up with
electric immersion in very cold weather if it is needed.

Since this is run as a bed and breakfast I would perhaps be thinking
of installing a second boiler to work in cascade with the other
so giving a backup should one fail.

One pump isn't enough. So I would pump two zones for central heating
with individual pumps and a third pump for the hot water.

Ideally install a low loss header to pump from to the zones.

If not already I would change to a sealed system.

 

[ALEC1]

Why wouldn't one pump be enough..a 15/60 should do it no problems...

 

[Rickf29]

Thanks for the feedback guys. The main problem I face is lack of funds on their part. I realise this is neither your problem or mine but in trying to do a favour i'm going to struggle to get it put right as it should be.

At present they will not be able to afford a second boiler as good as that would be for them. Business is slow and they are on a tight budget.

To get it right in my head you are suggesting branching off of the main 28 mm flow with 3 circuits each pumped individually to get a decent flow rate? Could this be increased to 4 to allow the 2 new cylinders that are a good 30m away from the existing cylinder to have their own zone? Or perhaps if as alec suggest maybe 4 zones with a pump for the 2 Ch and a pump for the 2 HW?

Never fitted a low loss header before to be honest, I understand its a way to keep the flow of water at the right temps?

As for pressurising it that has been a thought but after seeing the existing pipework coming out of the concrete floor and knowing they have had rotten sections cut out i fear it could lead to a nice sprinkler system.

 

[ALEC1]

I am not a great advocate of zones... TRVs and judicial balancing will achieve the same effect....

its probably a bit of an art to get right on a system thats been added on to, but it must be possible...

 

[polesapart]

I would follow dcawkwell's good advice.

 

[ALEC1]

starting with a correctly sized pump a 15/60...

 

[gaswizzard]

25/80 would be somewhere near the mark for starters.

 

[ALEC1]

how come GW, I was always taught 15/50 up to 24kws, and a 15/60 for 30 kws.

According to that formulae, the root of the problem sounds like although the boiler is 30kws, and the rad sizing about the same, the pump is undersized..


changing the head is a low cost option..the op probably has one in the back of his van...also I am advocating ensuring the heating works with the hot water closed down, tne giving it hot water pririty...

 

[ALEC1]

If he wants to run everything at once a 25/80 may well be the solution, but he still needs to balance the whole lot...

 

[Rickf29]

Thanks all for your advice. Just to clear a few things up if it may help. Alec im not too sure how successful balancing would be as the new 12 rads are fitted into the main flow before the old zone control so they come on when HW or CH is called for in the old system. Coupled to this in now 2 new cylinders also drawing on the uncontrolled leg of pipework.

I hoped by zoning it better with a decent programmer that we could time it so that although the boiler is on the brink of being powerful enough they are not all calling at the same time, thus giving the heating a chance to get hotter quicker when all 100k btu is aimed at them and not split off for 3 coils also.

Cheers all

 

[ALEC1]

How ever you zone it the system still has to be balanced for the moment of maximum demand...you won't be happy unless that is done....Hot water priority just limits the demand to either the radiators or the hot water making things much easier...as cylinder coils have much less resistance than pipe work and valves...