Trying to balance new boiler not properly setup by installer

[Kaymo]

Hi,
Looking for some help in balancing the central heating system. I understand the basics of how to balance a system but I am a little baffled by some of the contradictory info out there! I have made some assumptions below, happy for anyone to correct me if I am getting this wrong!!

Boiler is a Worcester Bosch Greenstar 42CDi combi. It is new, less than 6 months old and yes it should have been set up properly by the Bosch W approved heating engineer, long story but as he is not answering the phone about the magnetic filter that he was supposed to fit I doubt he is going to entertain me about the system not being balanced properly. I know from watching him that his version of balancing was to twist a few of the valves before rushing out the door and that he didnt measure any temp drops, and from the fact that the last radiators in the loop are not heating up properly I started to look into the balancing myself.
I believe that the temperature drop across the system should be 20 degrees but most of the stuff I have read seems to refer to balancing radiators with a temperature drop of 11 deg. I think this is to do with older versus condensing boilers but from some of the posts here I have read I understand that the radiators may be designed for a 11 deg drop. They are older radiators mostly, about 20 in total.
This is part of what is confusing me, should I be setting the drop to 11 or 20 or something in between?

Also, I have already started to balance based on what I know and this has improved things, particularly with respects to the upstairs radiators heating up but I want to set this up properly and should I be going back to the start and checking the temperature drop across the system with all valves fully open. If this is not 20 deg does this mean the pump is not set correctly and is this something that I can adjust myself on this system (I think it is internal to the boiler)?

Sorry for the long post, appreciate any thoughts.

 

[twgas]

go for 20° drop.

 

[Mark Br]

Loin the sticky at the top of this board, detailed instructions there

 

[dcawkwell]

So much for Worcester approved installers.

 

[expertgasman]

So much for Worcester approved installers.

Th e problem is tht "approval" is earned by sales, not neccesarily skill. It shouldn't be allowed, as it is misleading to the consumer

 

[Kaymo]

Thanks for the replies guys.

I took a look in the sticky but one of the 1st things it says to use a drop of 12 deg C which is in conflict with the differential for the boiler of 20 deg C stated in the Worcester manual. twgas said 20 deg drop, do you mean C or F?

The sticky doesnt mention anything about checking the drop at the boiler, other guides I have read have said to check this with all the valves open and adjust the pump speed. Is this something I need to worry about or is likely to be ok? Should I just adjust the radiators and then check that the boiler has a 20 deg C differential when I am finished?

 

[spudkey]

I presume this boiler has been sized for hot water demand, How many rads do you have,
I doubt you will ever see a 20 deg drop

 

[Kaymo]

There are 20 radiators. Its a 100 year old house with high ceilings and large rooms hence the number of radiators. Why do you say that I wont see a 20 deg drop do you think that the boiler is oversized?

 

[bhm1712]

what are you using to measure the temperature? IR thermometer??

open all TRV's to maximum (or take off the heads)

open all lock shield valves on the radiators (make sure all rads have wide open valves both sides basically)

Start with the first radiator on the system and adjust the lock shield valve on the return pipe until there is a 20 degree or 11 degree (whichever you decide to go for) difference between flow and return. IR thermometer is easiest to do it quickly!

Once that one is done move onto the next one in the system and carry on until you reach the end.

Also, is the pump an external one or internal to the boiler? if external check which speed it is on, as i suspect a house that size will need max speed and probably even a 15/60 pump.

If you follow that procedure and still cant get the last radiators to heat to max temp then the installation is faulty in terms of sizing. You asked if it may be oversized, its more likely undersized at 30Kw if the house is as big as i think it is, and has 20 ish rads. My mother has a 36kw boiler for 17 radiators and British gas initially fitted a 24Kw boiler which they had to rip out under warranty because they sized it wrong. No matter how much they tried to balance, they couldnt get the heat to the last few rads and when hot water was on....well lets just say it didnt work

 

[ALEC1]

you can undersize boilers quite happily if you use compensation controls...full load is only really needed to bring a house up to temp when it is -3c both inside and outside...

going for a fixed delta t is a thankless task, again with compensation controls (and probably on-off too) all the condensing boileRs I see work with a delta t as low as 6c

if i were you I would just balance the system to get it working....

What is true is that some boilers only allow a maximum delta t accross the heat exchanger of 20c to avoid thermal shock.

and as it happens a radiators heat output is increased if that has a small delta T...and this results in reducing the burner rate, increasing boiler efficiency..

do the whole lot at low temperatures with compensation controls and you get a decent heating system!

 

[Agile]

To the OP.....

You need a contact thermometer to measure rad flows and returns. An IR type is useless!

Non conds boilers need 11-12 differential and conds boilers about 15-20 C.

Quick balance is to close all lockshields and the open each just one turn!

As stated Worcester list installers who just fit a lot of their boilers and NOT those who do the job properly.

Tony

 

[Kaymo]

Thanks for the replies all. I am using an IR Thermometer, I have had to put masking tape on to the pipes to get a good reading but it seems to be fairly consistent

I understand how to balance the system, the thing was confusing me was whether I should be using a 12 C or 20 deg C drop but my understanding now is that I work to the boiler spec which is 20 deg C differential. I am currently balancing the system to just under a 20 deg drop across each radiator. In rooms where the radiators are a bit undersized for the rooms I am making the drop slightly less. When I am done I will check the boiler differential and that all rads are heating equally and hopefully all will be close enough.

I am not too worried about the boiler being slightly undersized. The reality in normal operation is that we would only have about quarter to half the rads on. The majority of the TRV's are usually set to 1 or frost and only about 4-6 rads are fully on most of the time.

Its a bit of a minefield with trades unless you know someone from experience. I'm new to the area so when the quals check out, they have manufacturer approval, and this guy was even on which local with 5 stars, so what more can you go on. When he left I had to bleed the system myself as there was so much air in it that three of the rads were cold, then I phoned him about the magnetic filter he was supposed to fit and he doesnt even answer the phone. I also noticed that he left the heating temp on the boiler at its max which if what I have been reading on these forums is correct may not be the ideal set up to make best use of the condensing boiler.

 

[Agile]

Thanks for the replies all. I am using an IR Thermometer, I have had to put masking tape on to the pipes to get a good reading but it seems to be fairly consistent

I am not too worried about the boiler being slightly undersized.

The IR may give a consistent reading but is unlikely to be accurate ( unless you paint your rads matt black! )

A cheap thermocouple probe and meter is less than £20 at Maplins!

Your boiler is seriously OVERSIZED for heating! Thats because its specced for hot WATER!

You need to set the boiler CH temp to about 70 C if you want it to be efficient.

I appreciate how difficult it is to get a good engineer! Even the ratings are not reliable as you have found.

Anyone who installs a boiler, leaves without checking its working and adjusted properly and then does not answer the phone is a cowboy and you should be giving him appropriate feedback! Did he even fill in trhe Benchmark and notify Building Control?

Tony

 

[ericmark]

I have just answered another thread about the same problem so please look at //www.diynot.com/forums/plumbing/7mm-or-15mm-copper-or-polyplastic.303201/ rather then me cut and pasting same info.

 

[D_Hailsham]

Boiler is a Worcester Bosch Greenstar 42CDi combi.

A combi boiler has to be sized for the Hot Water requirement. This means that, in most cases, it is oversized for the heating requirement. Use the
Whole House Boiler Size Calculator to find out your heating requirement. Set the Domestic Hot Water Allowance to 0 as you have a combi.

Let's clear up the 11/20 degree confusion. It's not so much that the rads are designed for a particular temperature drop as the fact that the output of a radiator varies with the water temperature.

Years ago, rad outputs were measured with flow of 90°C and return of 70°C. i.e a 20°C difference. The high temperatures were used because most boilers had cast iron heat exchangers, which would get damaged if the flue gases condensed.

A few years ago a new Standard was published BS EN442 which said that rads must be tested with flow of 75°C and Return of 65°C - a 10°C difference. The net effect was that the quoted output of all rads reduced by 11% overnight.

Condensing boilers need the return temperature to be below 55°C for condensing to occur. So, if the flow is maintained at 75°C, the difference is now 20°C. Unfortunately this means that radiator outputs are reduced by about 15%.

To find out if you can run your rads with a 20°C differential you need to make sure they are large enough. Use the Stelrad Elite Catalogue to find out the total output. (If the exact size is not listed you can proportion from the nearest size.)

It the rad total is equivalent or less than the calculated boiler size, they will not give out enough heat for very cold weather, if they are balanced with a 20°C differential.

If, on the other hand, the rads are 20%, or more, larger than the boiler size, you will be able to balance the system with a 20°C differential.

See How to balance a CH system