Hot water problems may occur in both the water supply and the central heating systems.
WATER GETTING TOO HOT
If the water is too hot, the most likely reason is that the thermostat on the cylinder is set too high or that the thermostat itself has malfunctioned. Where the temperature is set too high, the simple remedy is to adjust the thermostat setting. This needs to be done with a screwdriver. Isolate the power before adjusting an immersion heater thermostat, as you will need to remove the top cover from the unit (see Figure 2.7). You won’t need to isolate the power if a central heating cylinder thermostat has been strapped to the side of the cylinder.
In both cases, set the temperature to provide water at 60°C at the top of the cylinder (see Chapter 2). If, however, the thermostat has malfunctioned and simply fails to operate and close off the heat source, the thermostat probably needs to be replaced. This is a relatively simple process, making the electrical connections with a similar replacement component, but you will need to isolate the power before doing this. This will be discussed further in Chapter 8.
Remember this
The ideal storage temperature for domestic hot water to be drawn off at the taps is 60°C. Storing water too hot leads to the risk that someone could be scalded; in hard water areas there will be the additional problem of scale build-up. Storing the water not hot enough may lead to the growth of Legionella bacteria.
NO HOT WATER OR CENTRAL HEATING
A lack of hot water or central heating could be due to one of several possibilities. You may have hot water but no heating, or vice versa. There may be a blockage within the pipeline, such as limescale or sludge build-up, but this type of problem is fairly uncommon. The most likely cause, and the first thing to investigate, is an electrical control fault preventing the power reaching the point where it is required. The areas to investigate are:
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C a blown fuse or loss of power supply C
C the time clock/programmer wrongly set or faulty C
C a faulty thermostat (room, cylinder or immersion heater thermostat as appropriate)
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C a faulty motorized valve C
C a fault with the boiler or pump.
Electrical faults generally require the assistance of an expert.
The engineer will go through the above list and, by a process of elimination, find where the fault lies.
The power supply to the boiler and pump ultimately follows a set route (see Figure 5.3), and in order to determine the cause of a problem you will need to check that power is going to the first component, then that it leaves that component to move on to the next component, and so on until it reaches the boiler and pump. Along the way you will discover where the interruption in the sequence occurs, so you can focus on the area causing the fault. So, for example, if you find that 230 volts is going into the cylinder thermostat yet there is no voltage coming from it, this suggests that this component or the wiring to or from it is at fault.
power
supply fuse cylinder
thermostat motorized valve
boiler pumpand motorized
valve thermostatroom
programmer
Figure 5.3 Sequential flow diagram showing power supply to the boiler and pump
RADIATORS NOT GETTING HOT
If the radiators fail to get hot, this may be the result of an electrical fault as discussed above. However, assuming that you have an electrical supply to the pump and boiler, it might be a problem with the pump itself. You can check whether the pump impeller is going round simply by placing the end of a large screwdriver up against the pump and putting your ear to the handle. This transmits the sound along the screwdriver shaft to the handle and you will hear whether the pump impeller is going round.
You can investigate the operation of the impeller further by removing the large central screw from the body of the pump,
out of which a little water will discharge. Behind this big screw you will see another smaller screw head that will be rotating if the pump is in operation. If not, try to turn it with your screwdriver; if you are lucky, it will start up and flick from your screwdriver as it rapidly turns. In this case, replace the outer large screw to stop the water seepage. I hardly dare say it, but giving the pump a quick tap on its side with a hammer will sometimes nudge a pump back into action. If the impeller fails to turn, it will need to be replaced.
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C Replacing the central heating pump
Once you have decided that the pump is faulty, you will need to buy a replacement of a similar design. The task, summarized in Figure 5.4, is then completed as follows:
1 Remove the electrical power supply to the pump and boiler by isolating the circuit and removing the fuse. Once you have confirmed that the power is dead, remove the old wires where they enter the pump.
2 If you are lucky, there will be a water isolation valve on either side of the pump. These are operated by turning the two slotted heads on the valves one-quarter of a turn with a screwdriver or spanner. Where there are no isolation valves, or these are ineffective, you will need to drain down the whole heating system (see Chapter 4).
3 With the water isolated, you can now undo the large nuts on either side of the pump and remove it.
4 With the old pump out, position new sealing washers, if these are used for the mating surfaces, and use a little jointing paste where the components meet as the new pump is inserted.
5 Firmly tighten the joints to secure the new pump in position.
6 Now turn the water supply back on and check for leaks.
7 If all is sound, you can remake the electrical connections and test the system.
Remember this
If in doubt over the electrical wiring to the circulating pump, you must seek the advice of a competent electrician. Failure to observe this simple rule could put you and others in danger of electrocution.
RADIATORS DON’T GET HOT, BUT THE PUMP IS OK
If the radiators fail to get hot but the pump is working, the system may be blocked with sludge caused by corrosion. Should this be the case, you will need to descale the system using a special acidic solution to dissolve it, as discussed earlier.
Sometimes a radiator only gets warm around the sides and along the top and has a cold spot in the middle. This is a classic valves turned off
to isolate water supply when replacing pump
pump
ensure you fit a new sealing washer
to confirm pump is working remove this screw to view rotating head below
Figure 5.4 Replacing a central heating pump
Once the new pump is in place, the speed, if it is a variable-speed pump, will need to be set to the lowest setting and only increased if all the radiators fail to get hot. Setting the speed too high might create unacceptable noises within the system.
sign that corrosive sludge has accumulated in that particular part of the radiator. Again, it may be possible to solve this problem by using a descaling solution. Alternatively, the radiator can be removed and subjected to individual treatment and flushing through with a high-pressure hose.
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C Bleeding a radiator
There may be just one or two radiators on your system that are not getting warm. Assuming that the valves at each end of the radiator are open, the first thing to check is that they are not cold simply because they are full of air. Air is expelled from the system radiators through a small air-release valve located at the top and to one side of the radiator, a process referred to as
‘bleeding’. Do this as follows:
1 Turn down the room thermostat. This will turn off the pump. (The reason for turning off the pump while bleeding the radiator is to ensure that air is not sucked into the system if the pump is creating a negative pressure within.)
2 Use a special square-headed radiator key to open the air-release valve, turning it anticlockwise. You will hear the air being forced out and eventually water will appear at this point, whereupon you simply close the air-release valve.
3 Turn the room thermostat back to the desired setting.
If a particular radiator continues to accumulate air, this suggests that air is being drawn into the system, possibly due to the incorrect positioning of the circulation pump. This situation must be addressed because the air that is being drawn into the system will speed up the corrosion process and very soon you will be experiencing leaky radiators that have corroded from the inside. Correct pump location has already been discussed in Chapter 3.
If some radiators still remain cold after bleeding, the system might be too large for the pump. A particular pump only generates so much pressure and will only push the water so far, so a larger pump may be required. The pump may have variable settings and it might be possible to increase its speed
and pressure by making a simple adjustment on the side of the pump itself.
Another possibility is that some of the radiators closer to the pump have their lockshield valves open to such an extent that they are taking all the flow of water, in which case they need to be closed a little in order to balance the system (see Chapter 3).
A simple test to see if balancing is required is to close off the manual radiator valve operating heads to several radiators that are working fine, to see if the cold radiators then get hot; if so, you need to balance the system better.
LEAKING RADIATOR VALVE
Sometimes when a radiator valve is operated, it leaks from the nut at the point where the spindle turns. This can only be seen when the plastic head is removed. This leaking joint is often the result of the valve not being used regularly. The simplest cure – and often all that is required – is to tighten up the gland nut (see Figure 3.11). If this does not cure the problem, the gland will need repacking. To do this, take these steps:
1 First, turn off both radiator valves. To close the lockshield valve you will need to use a small spanner. When you close the lockshield valve, count the number of turns it takes and, when required, only open the valve by that number of turns.
2 With the valves closed, simply unwind the gland nut, pack a few strands of PTFE around the spindle and push it into the void into which the packing gland nut screws, poking it down with a small screwdriver.
3 Now replace the packing gland nut, tightening it just enough to squeeze the new packing material within the gland.
4 Re-open the radiator valves and test it.
Repacking this gland nut is basically the same procedure as repacking any gland, as described with reference to a leaking stopcock or tap in Chapter 4 (see Figure 4.11). Note that some designs of valve do not have a gland nut and use an ‘O’ ring. If this joint leaks, the valve will need to be replaced.