Does my Central Heating system need to be balanced?

[xyza]

How many rads do you have, what type and what size?

8 rads
80x50 double (1 set fins)
50x80 single (1 set fins)
50x60 single (1 set fins)
60x60 double (2 set fins)
130x50 single (1 set fins)
50x80 double (2 set fins)
50x50 single (1 set fins)
50x70 double (2 set fins)

I'm wondering if there is a bypass.

How do I check if there is a bypass?

 

[xyza]

Your boiler has a fixed output, which is set when installed by adjusting the gas pressure. When it is firing it runs at the preset full output.

So is it possible that the engineer on the last service may have also adjusted the gas pressure? (ie in addition to the burner pressure?) or can this only be set on installation?

 

[D_Hailsham]

1. Your rads have a total output of about 7.1KW. This is less than the boiler can produce (8.79kW max), but that's OK as the extra heat will come in useful when the HW cylinder is being heated.

2. When I said "Your boiler has a fixed output, which is set when installed by adjusting the gas pressure", I really meant the burner pressure; the gas pressure is set at the gas meter. Sorry for the confusion.

3.Bypass

Is there a pipe connecting flow to return with a valve on it? It usually tees off the pipe connecting pump to motorized valve(s) and connects to the cylinder return.

At the beginning you said that the differential at the boiler is 12C, but the rads vary between 2C and 7C. This certainly suggests that there could be a bypass, but it could also mean that the HW cylinder is grabbing too much flow. Have you checked the balance with HW turned off and with it on? It could be that the flow through the cylinder needs to be reduced - there is usually a valve on the return.

 

[xyza]

Is there a pipe connecting flow to return with a valve on it?

Bypass – can’t see anything that looks like a bypass and also can’t see any valve on the return from the cylinder. The set up seems to be such:

Flow from boiler runs upstairs into the Aerjec, which has a flow output into the pump, in turn into the 3 part valve, which in turn goes one way to the cylinder and the other to the heating system. The temperature in all these pipes is within 2-3 degrees of each other (approx 75C). In addition there are also 2 other flows via the Aerjec :

a) directly up into the loft and over the top of the small tank (temp approx 70C) (but water in the tank is cold), and
b) via a long downwards facing loop (with a drain pipe at the bottom) which then loops back upwards into the loft going into the bottom of the small tank in the loft. The temp where it leaves the Aerjec is approx 75C but this temperature rapidly falls as it drops down the loop until it is “cold” in the uphill part of the loop.

Flow from the 3 part valve for HW goes into the cylinder about 2/3 way up the cylinder, with a return from the cylinder exiting at the bottom (temp appox 71C). A pipe from the top of the cylinder runs into a tee joint, one end going into the loft, the other to the household taps. In addition there is a pipe exiting the back of the tank (bottom) which runs into the loft and has a red wheel valve in it (impossible to turn!) - I think this was from the old immersion heater - this pipe is always cold.

Have you checked the balance with HW turned off and with it on?

The differential in the rads is the same whether just CH or CH&HW. The differential at the boiler seems to be slightly greater (ie 10-12C) when HW is on rather than only CH (ie 7-9C). It is really difficult to get accurate measurements as the boiler is on and off for such short periods.

At the minute the pump is turned down to 1 and the boiler stat turned down to 2 which seems to be helping with the ambient temp in the house (rads seem to hold their heat a while longer) but is still doing nothing to improve the slow warm up time. (Not sure what will happen at these low settings once the weather turns really cold).

Sorry for the confusion

No need to apologise - you have been a great help to furthering my understanding of system/rads input/output and boiler pressure/input/output for my particular boiler. I believe I now have this clear, my understanding being that:
a) boiler input is directly related to the pressure of gas coming from the gas meter and this pressure cannot be altered at the meter or in the boiler by the heating engineer (any variation in gas pressure at the meter I assume is due to the national carrier)
b) this input is turned into boiler output by adjusting the burner pressure on the boiler but cannot be altered in any other way
c) the only adjustment available on my boiler is the burner pressure (no other settings/adjustments/changes - including at the boiler gas valve - can be made)
I would appreciate if you could confirm that my understanding is correct as this has been a puzzle to me throughout. (Thank you).

 

[D_Hailsham]

can’t see anything that looks like a bypass and also can’t see any valve on the return from the cylinder.

A bypass hasn't been installed as you have a 3-way. At least one port is open, providing the required flow back to the boiler when the pump overrun is working.

Aerjecs have been known to clog up, reducing the flow.

The orientation of the Aerjec is important for correct operation. It should be as in either of these pics

View media item 67952
The two pipes going up into the loft are the vent (hangs over the feed and expansion tank) and the feed (connected to bottom of FE tank).

The pipe going into the bottom of the HW cylinder is the cold feed from the large cold water tank in the loft. The red valve is there so you can isolate either tank or cylinder.

The pipe going into the loft from the top of the HW cylinder is the safety vent - it hangs over the cold water tank.

return from the cylinder exiting at the bottom (temp appox 71C).

I assume 71C is the return temp, what is the flow into the cylinder?

What are you using to measure the temperatures?

At the minute the pump is turned down to 1 and the boiler stat turned down to 2

2 is the recommended setting for summer use when only the cylinder is being heated. In the winter it should be set to Max.

Do you have a room thermostat?

 

[xyza]

Aerjecs have been known to clog up, reducing the flow.

Aerjec orientation looks ok. Any way of checking if its clogged short of cutting pipes around it?

I assume 71C is the return temp, what is the flow into the cylinder?

Sorry - yes 71C is the return, flow into the cylinder is 77C.

What are you using to measure the temperatures?

An infrared thermometer placed directly against pipes (either painted pipes or with tape on them where these are not painted).

2 is the recommended setting for summer use when only the cylinder is being heated. In the winter it should be set to Max.

Boiler stat has always been left on max winter & summer alike (pump on 2) until all this trouble started. Have experimented leaving boiler stat on max & pump on 3 = worse situation of all (quick blasts (1-2mins) of red hot radiators - almost like a "wind" coming from them- followed by rapid dropping of temp until they are totally cold for a considerable time, leaving room temps to also drop considerably). Gradually reducing both leaves rads warmer for longer so providing a more stable room temp. I'm concerned that if/when I have to raise the boiler stat back to max I'll get this same rapid rise & fall.

Do you have a room thermostat?

Yes - mechanical type fixed at top of stairs (ridiculous location but has always been there & worked fine in the past). This was swapped out to check if it was faulty - the new one made no difference

Any chance you could confirm my understanding that the burner pressure is the only adjustment that can be made on my type of boiler please? (I want to rule out problems at the boiler in my own mind).

If reduced flow through the system is the problem how could / would this be checked & determined?

 

[JohnD]

What colour is the hot water cylinder insulation?

Does it have a strap-on thermostat, and what temperature is it set to?
http://www.screwfix.com/p/honeywell-l641a-cylinder-stat/40051

Does the flow pipe to the cylinder go cool once the cylinder is hot?#

Is the tap water scaldingly hot?

On your 3-port valve, how hot are its three pipes, and does this change?
http://www.screwfix.com/p/honeywell-v4073a-3-port-motorised-valve/31421

 

[xyza]

What colour is the hot water cylinder insulation?

Thick compressed 'foam' insulation in a "digestive biscuit" colour.

Does it have a strap-on thermostat, and what temperature is it set to?

yes - 50C

Does the flow pipe to the cylinder go cool once the cylinder is hot?

Not immediately - stays hot (approx. 50C) for some time. If HW has not been requested it is cold.

Is the tap water scaldingly hot?

No - same temp it has always been - comfortable.

On your 3-port valve, how hot are its three pipes, and does this change?

All 3 pipes approx. 75C (peaking at 80C). It changes depending if HW, CH or both are being called for. However when only HW is on there does seem some "seepage" along just the first 10-15cm of CH pipe after it leaves the 3part valve. CH had switched off and the 2metres of visible CH pipe after the 3part valve by this time had dropped down to approx. 50C (from its previous 75C along the entire length with CH on). Switched HW on and pipes from 3part valve to HW & Pump rose to 75-80C. However temp in the CH pipe also went up to approx. 70C but only for about the first 10-15cm length after leaving the valve after which it then dropped to the 50C it had been along the rest of the length.

 

[D_Hailsham]

Aerjec orientation looks ok. Any way of checking if its clogged short of cutting pipes around it?

Use a magnet to check the Aerjec and connected pipes. Any blockage will probably be magnetic, so the magnet will adhere to the copper pipe.

An infrared thermometer placed directly against pipes (either painted pipes or with tape on them where these are not painted).

That should be OK. You can get some strange results from shiny copper pipe if you don't wrap tape round it

Boiler stat has always been left on max winter & summer alike (pump on 2) until all this trouble started. Have experimented leaving boiler stat on max & pump on 3 = worse situation of all (quick blasts (1-2mins) of red hot radiators - almost like a "wind" coming from them- followed by rapid dropping of temp until they are totally cold for a considerable time, leaving room temps to also drop considerably). Gradually reducing both leaves rads warmer for longer so providing a more stable room temp.

There's a lack of circulation - either blockage or the pump is knackered

Room stat - good

Any chance you could confirm my understanding that the burner pressure is the only adjustment that can be made on my type of boiler please? (I want to rule out problems at the boiler in my own mind).

Correct, the burner pressure is the only adjustment available.

The heat exchanger could be blocked.

 

[xyza]

Further update:

Does the flow pipe to the cylinder go cool once the cylinder is hot?

Flow pipe actually remains at approx. 50C for several hours (overnight) while the cylinder is hot and no water has been run off (slightly warmer at the cylinder end rather than the 3part valve end of the pipe). Once some hot water has been run off the pipe goes cold.

On your 3-port valve, how hot are its three pipes, and does this change?

In addition to the observations above there is also some slight "seepage" along the HW pipe when only CH is on (approx. 50C for about 10cm of pipe from the 3part valve)

 

[xyza]

Use a magnet to check the Aerjec and connected pipes.

Ok will get a magnet and try it out.

There's a lack of circulation - either blockage or the pump is knackered

Pump sounds ok - therefore suspect probably a blockage (would a plumber be able to "easily" find a blockage?)

The heat exchanger could be blocked.

How is this checked?

Correct, the burner pressure is the only adjustment available.

Thanks

 

[JohnD]

A powerful magnet is good for finding blockages of black magnetite (which can be soft sludge, but also forms hard blockages, possibly when it combines with limescale. Test around your air separator, and also where the cold feed and expansion pipe from the loft tank joins the main circulating pipes, and the pump valves, these are common places for sediment to accumulate.

Modest soft sediment can be removed with a DIY chemical clean at low cost, and this will do nothing but good, but a severe one usually requires the blocked parts to be removed and poked clean or replaced with new. It is quite expensive to have a powerflush to "wash through" your radiators, pipes and boiler with a chemical cleaner using a big pump. I have used various DIY methods and had good results on cleaning pipes and radiators, but don't believe they will get an iron heat exchanger in a boiler clean. Deposits in here lead to banging or bonking noises when the boiler fires to hot.

A system filter and corrosion inhibiting chemicals do a good job of keeping a clean system clean, but your is probably worse than that.

 

[Agile]

Deposits in here lead to banging or bonking noises when the boiler fires to hot.

Bonking in my vocabulary has a different meaning!

An IR thermometer has little practical use for balancing heating systems. A digital contact thermometer is the thing to use!

Reading the many posts brings me to the conclusion that your only problem is a lack of heat output from the rads.

Nevertheless, your system should ideally be balanced correctly so that the diff across each rad is 12 C or 20 C according to the boiler type.

Tony

 

[xyza]

Slight magnetic force on the "blue" part of the Aerjec and on the pump casing and the large nuts holding the pump in place. Is this because these items are made of a different (magnetic) material or is it likely to indicate blockages?

No magnetic field found in any other pipes.

Boiler makes a slight kettling noise but otherwise its quiet (ie no banging or knocking noises).

 

[JohnD]

Slight magnetic force

are you using a magnet (correct) or are you using a magnetic field detector (incorrect?)

The pump is almost certainly made of cast iron so a magnet should be very strongly attracted to it.