Boiler & Central Heating FAQs

[DIYnot]

1 ) WHICH COMBI BOILER?

[NB this list is highly contentious and changes rapidly as new models show their colours]
***Since this was written, opinons whave swayed around, so the list has been removed.***

To get the correct size boiler use the Boiler Sizing Wizard OR Boiler Size Calculator

When replacing a boiler, the quality of the installer AND the quality of the installation always determines how reliable the boiler will be.

Also, it is imperative that the system is properly flushed out and installed by a Gas Safe fitter.

Equally important is to protect the system with a good quality inhibitor such as Sentinel or Fernox. Inhibitor strength should be checked annually, and redosed every 3-4 years.

Good practice to have your boiler serviced annually too.

 

[FAQ]

2) RADIATOR PROBLEMS-

1) Radiators are cold at the top Try bleeding. See FAQ 4

2) . Some rads are not heating up or are only warm. Try balancing the system See FAQ 5


RADIATORS NOT WORKING- a checklist

1) Radiator valves are not open or TRV stuck. See FAQ 6

2) Pump not working or needs bleeding. See FAQ 9 & 14

3) Air lock in heating pipe work (not radiators). Turn off all the other rads to force the flow into the cold one.See FAQ 21

4) Zone valve or 3 port valve not opening allowing flow to radiators on Y plan or S plan systems. See FAQ 10 & 17

5) Check there is enough water in the system.
For a vented system check the F & E tank has water. In a sealed system the boiler pressure should be 1 bar

6 )Check the bypass which should only be open just a little.

An open bypass provides an easy route for the water back to the boiler without going along the full length of the flow and return pipes. This means rads furthest away will stay cold.

7) Sludge in radiator or pipe work or valve causing blockage which needs treating with a desludger and then flushed out. See FAQ 26

8 ) Newly installed rad not heating up

Could be that the boiler is stretched to capacity and can`t cope with the extra radiator,or the distance from boiler to last rad. It all depends on the size in kilowatts of your boiler and the number of radiators you already have.

Alternatively the rad has probably been piped up by teeing off an existing radiator (not ideal!)Better to feed from 22 mm pipes which will give better flow.

9)Check the Flow through Heating pipes - The "BUCKET TEST"

 

[FAQ]

3) DRAINING DOWN YOUR CH SYSTEM

If you wish to modify your CH pipework or change valves etc you will always need to drain down your system. This can be partial or full drain down depending on what you are planning to change.

1) Turn off boiler

2) If a vented system cut supply to the F & E tank in the loft.

3) You should find one of these valves (soldered and upside down) on your downstairs pipework:

https://www.google.co.uk/search?hl=en&q=drain+off+cock
Attach a hose to it (The other end goes into a drain outside) and open the valve. Water should exit out of the system and then open a bleed screw in an upstairs rad to vent it and speed up the draining.

4) DO NOT cut into any pipes until you are sure the system is completely empty or you will have an early shower!

When you have completed your work, add inhibitor, reinstate the water supply or refill if a sealed system to 1 bar and check for leaks.

ALTERNATIVELY.... hire / buy yourself a pipe freezing kit!

 

[FAQ]

4) BLEEDING YOUR RADIATORS

When water is added to a CH system, air finds its way in too. Air rises in water and collects at high points in the system, i.e. radiators and pipework.
Always bleed rads after refilling system or when you find the top of the rads are cooler than the bottom.

Frequent bleeding can mean you have insufficient inhibitor in your system and the air is in fact gas!

1. Switch off Central Heating and fit a rad key onto the bleed valve.

2.Wrap some cloth around the key to catch any expelled water.

3. Open valve by turning the key 1/2 turn anti clockwise - air being expelled will be heard.

4) Close valve when water starts to dribble out.

5) Top up boiler pressure to 1 bar if sealed system.


Bleed point above or will be found by feeling the rad top for a plastic cap covering the valve.

 

[FAQ]

5) HOW TO BALANCE A CH SYSTEM

If some of your rads are not getting their share of hot water you need to balance the system. This involves opening and closing rad valves to divert hot water so that all rads heat up more evenly.

Click HERE for details.


The Lockshield valve above is adjusted to control the flow to each rad.

 

[FAQ]

6) THERMOSTATIC RADIATOR VALVES STICKING SHUT.

POSTED BY CHRIS HUTT

These valves (TRVs) can stick in the shut position, resulting in rads remaining cold. More common in winter as they will have been off all summer. TRVs should not be turned fully off unless the rad is being removed and setting 1 or 2 is preferable.

To free a stuck TRV, first remove the plastic head from the brass body by unscrewing a knurled ring or nut. With the head removed you will see a small pin in the middle of the valve body. If you press this down with the flat of a screwdriver it should spring back to its original position. If the pin does not move the valve is stuck shut.

To free, keep applying pressure to the pin (gentle taps with a hammer), until the pin starts to move.

Do not pull the pin out or water will escape and it may be difficult to refit the pin. In most cases it is not the pin itself that is sticking, but the inner mechanism, so pulling the pin has no effect.
A few applications of pressure should free it. Open the head to the highest setting and refit.

 

[FAQ]

7) TEMPORARILY REMOVING A RADIATOR THANKS TO GAS4YOU

Firstly, put down a dust sheet underneath the radiator and a small plastic tray under the valve nut.Turn off the lockshield valve.
If you have a TRV at one end you will need to take the head off and fit a decorators cap to ensure it will not leak.

Undo valve nut between valve and rad slowly until water runs out. When water stops, open air bleed on rad to let more water drain out.

When water stops, lift one end of rad and drop over empty plastic tray to empty last bits of water. Be careful here as this will probably be black and/or rusty water.

When finished draining do up air bleed, undo other end valve nut, remove rad and turn upside down to eliminate drips from valve bodies. Fitting is a reversal of above.

You will need to top up system pressure via filling loop or filling link built into your boiler.

 

[FAQ]

8 ) REFILLING A SEALED SYSTEM

If you have a sealed combi system your pressure should be topped up to around 1 bar, (or consult your manual for the recommended operating pressure).

This is done via a silver braided pipe under your boiler in which the valve is opened to allow water through until you reach the correct pressure.More details here.


Valliant Turbomax needs a small key which is turned by a quarter turn or a screwdriver will suffice.

If you have a Worcester Bosch please see FAQ 16

Some GlowWorm boilers have a blue knob, others have a black plastic tap underneath - boilers vary.

Also read FAQ 15 for background

 

[FAQ]

9 ) BLEEDING A CH PUMP

All Systems:
Loosen the large silver/brass/black centre screw and allow air to escape until it starts to dribble water. Put screw back in.

Vented systems:
A pump won't pump if it has air in it. To vent, check where boiler pipes enter the hot water cylinder for a bleed point .

Check there's plenty of water in the header tank, and make sure you're bleeding the system with the motorized valve(s) open i.e. push small lever on end to "manual" position.

If all else fails consider turning the pump round to push the air to where it can be bled out - then turn it back again!

Sealed Systems:

Check that the Automatic Air Vent in or near the boiler has its cap LOOSE. There may be additional manual or automatic vent points.

 

[FAQ]

10) HOT WATER OK BUT RADS COLD (or vice versa) THANKS TO CHRISR

Usually down to motorised valve failure

This will work for fully pumped systems, for both a single 3 port valve or two x 2 port valves. Or a combination, come to that.

To get you warm, turn the cylinder thermostat right up to 70, and the boiler thermostat down to 1. Then put the CH valve lever (3 port valve lever) in the hooky place which holds it in the MAN position.

This is a "2 port" valve. "3 ports" have 3 pipe connections in a T shape. AKA diverter valves, mid position valves.

Turn the HW ON at the programmer.
The system will try to make the HW hot, but will fail to get hot enough because of the stat settings. Your rads will warm up and the TRVs
will still shut but the wall thermostat will do nothing.

If there's a little bump on the top of the motorised valve head (only Honeywell valves), it means you can remove the head from the body to replace it without getting wet. The mechanics of the heads do wear out and jam, but you can just change the motor (Synchron) which is sold widely.

YOu can change the synchron motor in situ, but it's easier to take the head off to change the motor and to get at wires, and then put the head back when done. If you change the motor with the head off, you can wiggle the lever to help seat the motor screws and central spindle connector.
A magnetic T15 Torx screwdriver is good for the motor and head screws though a flat bladed one will do.
Other makes vary.

Any water leaking from the valve body will have got into the head and switches too and rusted it, You will need to drain down and fit a new valve.
Also remember to isolate the mains power from the heating system before you start any work.


*If you have 2 , two port valves and have "lost" your hot water, the 2 port valve for the hot water may not be opening.
Temporary trick to get you some hot water:
If you latch the lever on the HW valve in the "Man" (partly open) position, the water will heat up whenever the CH is on. Turn the boiler temperature down ( to say 50 if marked) and the central heating on - make sure there's a call from the room stat.
Your hot water cylinder will get to the boiler setting after a while. The cylinder stat will do nothing.

*If you have 2 , two port valves and have "lost" your hot Central heating,
the 2 port valve for the hot water may not be opening.
>> Temporary trick to get you some hot radiators:
If you latch the lever on the CH valve in the "Man" (partly open) position, the rads will heat up whenever the HW is heating. Turn the boiler temperature down ( to say 50 if marked) and the HW cylinder stat to say 60. The HW cylinder, and the rads, will go up to 50 and stay there. The HW stat will never be "satisfied" & turn the boiler off.

*If you have a three port valve, (T shaped brass body) and the motor has failed, most will stay in the HW position. Your HW will work but you will have no Cental Heating. If you latch it in the MAN position, it will be open to both CH and HW. Use the procedure in the previous paragraph from >> to get you some hot radiators.

Valves can also fail in strange ways, eg internal switches fail.

 

[FAQ]

11 ) CENTRAL HEATING (F & E) TANK OVERFLOWING

If the smaller tank (which supplies the heating) is overflowing to outside you need to check the following:

1) Float valve has failed. Replace the washer or renew the whole valve.

2) The cylinder coil may have a hole in it. Water will pass from the cylinder (domestic tap water side) and into the central heating system.

To check this, tie up the F & E ballcock, or turn off the mains supply to it, and see if it still overflows.

3) Water level may be too high. It should be 4 inches deep with the system cold.

Remember, water expands when hot (hence the name for the tank) so a warm system will cause the tank level to rise anyway.

 

[FAQ]

12) BLOCKED C H COLD FEED - Thanks to ChrisR

A simple way to unblock a cold feed on a vented HW system:

Sometimes the blockage is surprisingly soft and this fix will blow it back up into the f/e tank where you can bale it out.
Make the connector from a flexi tap hose and a 15 - 22mm adapter, and a 22mm elbow, all Speedfit.

This method can be used to fill a system you can't get water into, e.g to bleed upper floor rads. It is NOT a long term solution however, as there is very little reserve of water to replace losses, due to a blocked feed pipe.

Open the mains supply tap in short bursts until the system is full, and then remove the temporary connection.

If this doesn't work there is no choice but to cut into the feed where it goes into the system and clear the blockage.

Feed/expansion cisterns should always have an overflow going to outside (not shown). The cold water level should be at least a couple of inches below the overflow so there's room for the water to expand when warm. More for big/old installations.

 

[FAQ]

13 ) BOILER MANUALS

Thanks to Gunslinger

HERE is a selection of installation / user manuals I have uploaded to Rapidshare. There is also a couple of fire manuals too.

 

[FAQ]

14) CHECKING THE PUMP IS WORKING CORRECTLY?

Thanks to Bengasman

Fixed/manually set speed pumps:

Turn boiler off at mains and set the timer for constant heating and room stat to max. Take out the big chrome screw in the middle of the pump and water should start to drip out. Be prepared to catch a cupful, some are faster than others.

Set pump to 1 and turn the mains back on. The pump should start spinning fairly fast.

Set pump to 2 and then 3 which should increase pump speed noticeably each time. Turn mains off, and replace screw.

This bleeds the pump of air but it may not be pumping effectively. It could be blocked, the rotor may have come off, the shaft may have broken or jammed. The only way to be sure is to separate the halves of the pump (Allen screws) and check that the rotor is hard to stop with say one finger.
Pump valves can also become clogged.

After screw removed you can insert a small flat screwdriver to feel shaft rotating. Sometimes a stuck pump can be freed this way.
Also some pumps have a centre screw with a plastic cap, which can be unscrewed but not removed.

 

[FAQ]

15) BOILER PRESSURE PROBLEMS - Thanks To ChrisR

Most Combi Boilers are Pressurised and this is shown on a gauge marked 0 -4 bar. There is often a red adjustable plastic marker on the gauge which does nothing!

If the pressure gets to 3 bar the “PRV” opens and allows water to escape to outside. However, once a PRV has passed water, it will tend to keep leaking, usually because of dirt on the valve seat and will need replacing. Sometimes by twisting the knob they may "snap" shut.

If you aren't sure whether it's "letting by" or not, tie a small plastic bag over it and leave it for at least a day. If there's water in there, empty the bag and leave it for longer. Like any drip, they sometimes stop if left alone. It has to stop completely though or it will need changing.


1) Pressure TOO LOW

Over time, water will escape and the pressure will drop, losing approx 0.5 bar in 6 months. When it reaches 0.5 bar or lower the boiler may stop. OR it may not stop even with the pressure reading zero.
If the pressure drops quicker than this you have a leak. Bleeding air from rads will also cause pressure loss.

2) Pressure TOO HIGH

This can occur if the Filling loop has been left connected and not quite shut. Or, the Heat Exchanger in the boiler has perforated and is letting tap water fill the system.

3) Pressure going right UP then right DOWN

When water is heated it expands and squashes the air contained in the “Pressure Vessel” usually inside the boiler. This pressure rises maybe 0.3 bar on heating, and drops again on cooling. On some boilers the pressure jumps up a little when the pump runs.

If all the air in the PV has gone, the water has nothing to squash and the pressure will keep rising to 3 bar which will activate the PRV and water will exit through the wall.

On cooling the pressure then drops and may go so low that the boiler turns off. This is often noticed when the Heating is turned on in Autumn because more water is being heated so there's more water expansion to accommodate. A behavior to note is the pressure rising very quickly on opening the filling loop.......
(Boilers vary enormously but if it goes up half a bar in a couple of seconds that's much too fast).

Solution is to Repressurise the Pressure Vessel.

For that see HERE