Central Heating - Expert Assistance Required

[TheScullster]

Hi all

I am trying to improve the operation of my central heating system and would appreciate the opinions of the more experienced group members.

The story is:

Originally 3 bed detached 1970s house.

Additions since built:

1 Kitchen extension with 1 rad single panel rad 1200 x 600 1 Back room extension with 1 double panel rad 1000 x 600 1 Bedroom/En suite with rad and towel rail (see link)

to image (which shows upstairs piping and radiators only), the problem is little heat to new bedroom rad 7 and almost nothing to towel rail

1. Downstairs main runs are 22mm, but upstairs is all 15mm. Not sure if it is significant, but the new part that hardly works is piped in plastic - see link for plastic/copper joint location.

Another factor that may affect the towel rail operation is the height. Somewhere I seem to remember reading that a certain distance was required between the top of a towel rail and the underside of the loft CH header tank. In my case this distance is approx 650mm.

I have tried major throttling of the downstairs rads to improve flow upstairs, but do not seem to be able to get acceptable performance of upstairs and downstairs rads to include items 6 and 7.

So the question:

Looking at the pipe runs and radiator sizes involved upstairs, are 15mm mains simply not up to the job?

Thanks to anyone who has even managed to read this far!

Phil

[dennis]

Do the pipes branch off from a 22mm feed or do they run in 15mm from the ground floor?

Have you tried bleeding the system? Have you tried opening (just a bit) the lock shield valves on 6&7?

[Doctor Drivel]

The inserts on plastic pipe reduce the 15mm to 12mm. This may contribute. Even if the pipes are too small for the heat load you should still be getting flow to all the rads. If all downstairs rads are off does all upstairs work OK? Have you increased the pump speed? Check the pump impeller, it may be shattered from debris in the system.

[TheScullster]

Haven't opened the boxing yet, but I'm pretty sure that the upstairs/downstairs split is half way up ground floor wall (heating solenoid valve is approx level with wall mounted boiler, believe the 22/15 split to be there also).

I have drained, refilled and flushed numerous times when replacing old rads.

Thanks

Phil

[TheScullster]

Not sure if inserts have been used! Tees are push fit Hep2o in main 15mm runs rather than compression fittings. How are these removed? I have heard mention of sliding collars but can't see them on this type of fitting!

I will try this. Not sure if I've tried this before or not! If flow is still not adequate, is it a mains size increase? If so, how much do I need to upgrade and is plastic the way to go?

Reluctant to do this as I have had pump over problems in the past! Is it likely that the two issues are related?

Thanks for help

Phil

[John Rumm]

Plastic ought to make no difference...

So long as when you bleed it you get water out of the top eventually then you ought to be ok.

It does sound like a balancing problem (or perhaps lack of flow from the pump in general - have you tried a faster pump speed (watch you don't cause it to start pumping over)))

It may be you need to go back and rebalance the whole system from scratch.

15mm is good for upto 6kW of total rad output and you are going to be nowhere near that...

[John Rumm]

I think that is a bit of a red herring anyway... yes the inserts will reduce the diameter a little, but flow resistance is a function of not only the diameter of the pipe, but also the length - and inserts are short. So a reduction to 12mm for a couple of cm every now and then will make a negligable difference.

Also note that your total heating load should still be satisfied even if you had a complete run of 12mm pipe - you only have a couple of not huge rads on this pipe run IIUC.

Could be...

It might be you need to tackle the problem with more pump speed and then sorting any pump over issues.

What make/model of boiler is it?

[TheScullster]

I believe that the pump over problems occur when hot water only is being heated in cylinder. The system is S plan with the hot water valve in the airing cupboard close to the tank. The CH valve is close to the boiler, I believe at the 15/22 upstairs/downstairs split. I think that pump over occurs when the CH stops calling for heat and only hot water demand remains. Have increased the height of the vent loop to the apex of the roof, but still seem to remember problems when running at pump speed 3.

Glow worm Space Saver 50 - yes I know this is old and a bit undersize after all the mods. I wanted to iron out the problems, then introduce new boiler and pump.

Thanks for input

Phil

[John Rumm]

I doubt that can be converted to sealed system operation (since that is an guarenteed way to fix overrun problems!), but it might be worth checking with Gloworm.

A new boiler will be able to run sealed anyway - so you could lose the vent and header tank etc anyway.

[TheScullster]

Must confess I am reluctant to take the sealed system route. Partly due to lack of confidence in existing within-concrete-floor plumbing. Partly from the safety angle - blocked relief valves etc. As stated, the house is 1970s build. Do you happen to know whether there were quality issues around this time for flux/solder. The original piping is bedded in sand filled channels wrapped in hession or similar. I seem to remember some problems with joints failing with age and spontaneously separating. After a failed 15mm elbow discovered soon after moving in, I am perhaps overly concerned about the possibility of a repeat performance. To be fair this was a fitting failure due to expansion rather than a failure of a soldered joint.

Phil

[Set Square]

Even a sealed system will run at a *lower* pressure than your mains cold water supply. Presumably that is ok?

[Phil Addison]

[snip]

Assuming no physical blockage the first step would be to check the balancing

have to consider the whole system not just the upstairs.

Balancing WILL allow you to get heat to all radiators, but that may involve turning the hot ones down to almost zero flow (and hence low output). Then you will know which runs are causing the low flow and be able to think about how to fix it. Once balanced, you can decide to sacrifice the rads on the bad run and open up the others again to restore heat to the rest of the house.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at editor (a t) diyfaq (stop) o r g (stop) uk

[Phil Addison]

Ahh... didn't notice you already suggested that.

That is the maximum heat load 15mm can carry, over some maximum given length of flow + return. Lower loads can be carried further. Sorry I don't have the actual lengths to hand.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at editor (a t) diyfaq (stop) o r g (stop) uk

[Doctor Drivel]

11C Temperature Difference Between Flow and Return (81C flow - 70C return)

Pipe Size (mm) - approx kW/hour

15 - 6.0 22 - 13.4 28 - 22.5

Pipe Size : Approximate Maximum Non-condensing Load

20C Temperature Difference Between Flow and Return (70C flow - 50C return)

Pipe Size (mm) - approx kW/hour

15 - 9 22 - 24 28 - 70

The condensing boiler can use 22mm pipe where 28mm would be required for a non-condensing boiler.

[Phil Addison]

OK, but what I am missing is the maximum length for each load, in particular the 15 and 22mm. It's normally readily available but my book has gone missing.

Phil The uk.d-i-y FAQ is at

Google uk.d-i-y archive is at editor (a t) diyfaq (stop) o r g (stop) uk

[Set Square]

What the hell's a kilowatt per hour? [Bearing in mind that a kilowatt in its own right is a measure of energy consumed/delivered per unit time]

[Doctor Drivel]

kW/hr & BTU = energy

Firstly, separate power and energy; this confuses many people. Energy is Power x Time. A BTU is energy. Put it over one hour (energy x 1) and we have "power"..... BTU/hr.

- The watt (W) - Is a unit of "power".

- kilowatt-hour (kWh) - This is a 'unit' of chargeable electricity and is a unit of "energy". Yiou buy energy. Power results from the energy.

The kilowatt (kW) is simply 1,000 watts. A traditional electric heater rated at 1,000 watts, or ten 100 watt light bulbs will consume one kilowatt (power).

In your electricity bill, what you pay for is the product of power and time. This is obvious - the one kilowatt electric heater on for three hours is going to cost three times as much as for one hour. Therefore the chargeable electricity 'unit', on your bill, is the kilowatt-hour (kWh). This is by tradition in the world of electricity metering called a 'unit'. What you are paying for is energy, rather than power

One unit of electricity (one kWh) buys you a:

- 1 kilowatt electric heater burning for one hour.

- 100 watt light bulbs burning for ten hours.

- 8 kW shower for seven-and-a-half minutes.

The one 1 kilowatt electric heater running for six hours would use six units, but if you left the 8 kW shower running for half an hour it would use four units.

Electricity meters give readings in 'units' (kWhs) directly. This simplifies bill calculations.

Gas is now charged for by the kWh too. 3412 BTU/hr = 1 kW

In relation to what a pipe can deliver in heat. The boiler took energy (gas or electricity) and turned it to power - or did it? This heat is fed to radiators. The heat travelling to the rads in the pipes is now energy as far as the rads or fan convector heaters are concerned.

A powers station takes energy, water, oil, or coal, burns the energy to make power, which turns the generator which produces energy, which goes down a cable to your house and turns an electric motor and produces power.

I think that is. It's late.

[dennis]

Could you explain why there is a difference between the condensing boiler and a non-condensing boiler? I can't see why there would be a difference.

[Doctor Drivel]

It operates at a wider temperature differential.

You can increase the efficiency of a non-condensing boiler. Insert a blending valve on the boiler return set to 60C (it doesn't go below dew-point inside the boiler). This is common practice with commercial boilers using a motorised mixing valve. This mixes system return water with flow water from the boiler. Design the system to run at 80C flow and 60C return, and balance the system to achieve 20C across the heat loads. I would only do this with a one-piece heat exchanger. You can then downsize the pipes. Note: the makers would always say runs at 80C flow and 10C temp differential. If you know what you are doing you can greatly improve efficiencies

[Dave Plowman (News)]

So a hydro-electric station burns the water?