Tutorial to repair the three-way valve for a boiler

Knowing how to repair a three-way boiler valve can save the day. As I’m sure you already know, when the 3-way valve is faulty, the heating and DHW installations communicate, and the radiators can heat up with the heating off, as well as almost cold water coming out of the taps when there is a demand for hot water. That is why in this article we are going to explain, step by step and in a simple way, how to repair a three-way boiler valve, so that the heating and DHW are back in order as soon as possible.

What is a 3-way valve and how does it work?

A 3-way valve (also called a diverter valve, or simply V3V) is just what its name says: a valve that has 3 inlets/outlets, and specialises in handling different fluids, either to combine them or to keep them separate depending on the flow, best suiting the specific installation in which it is placed.

The 3-port valves are part of the family of so-called multi-port valves, which can have 2, 3, 4 or more ports. Normally the operation of three-way valves is automatic, and they are widely used in heating and air conditioning.

They have a hydraulic component, but also an electrical component that is the one that controls the operation. For this, the valve is usually combined with solenoids or servomotors, which are responsible for automatically managing the inputs and outputs.

As for the typology of 3-way valves, there are several types. For example:

  • Mixers: They combine the fluids from two inputs and direct them to a single output.
  • Dividers: They separate the fluids from one inlet to two outlets.
02 Eolo standard 3-way monoblock valve Immergas 3010416_A for sale at Suner

Before repairing the three-way valve of a boiler: how to know if it has failed

To know if we need to repair the three-way valve of a boiler, the first thing, of course, is to know if it is faulty. There are several symptoms or indications that the V3V is defective. These symptoms are:

a) Hot heating pipes when we open the DHW

The easiest way to check for V3V problems is to turn off the heat and wait for it to cool down. Then we turn on the domestic hot water but not the heating. If the flow pipe from the boiler to the radiators gets hot, it is a sign that the 3-way valve is faulty.

b) Hot radiators with heating off

03 A man brings his hands close to the heat of a heating radiator

When we turn on the domestic hot water, the radiators heat up even if the heating is off. This occurs because the function of the 3-way valve is to manage the heating installation and the domestic hot water installation separately. If this valve fails, these facilities come into contact, or as they say, “communicate” and conflict. This can happen even if the 3-way valve is left open a minimum.

c) The hot water does not come out hot but lukewarm

That the hot water does not reach the selected temperature also occurs as a result of the heating and DHW circuits being connected. As a good part of the calorific power escapes towards the heating circuit, the hot water comes out lukewarm through the taps and showers, or it may even surprise us by suddenly getting cold while we shower.

d) There is hot water but no heating even if it is turned on

This happens when the 3-way valve in diverter function gets stuck in the hot water function, and although there is a demand for heating, it directs the hot water to the taps and showers instead of to the radiators.

e) You have to have the heating on for there to be DHW

It is the opposite case to the previous one. The 3-way valve in the diverter function got stuck in the heating function. If the seasons have come where we leave the heat off, and you notice that you don’t get hot water unless you also turn the heat on, that probably means the three-way valve is bad.

04 VC ZM G 6000 3-4'' 3-way valve BSTP T 65 Honeywell 9031_for sale at Suner.

Is it worth repairing the three-way valve in a boiler?

Obviously, if we know that repairing a part of the boiler is going to give it a considerable time of useful life, it will be worth continuing to use it instead of spending money on a new one. But it’s not always worth repairing.

3-way valves are precision parts, with sensitive gears that are prone to hardening, seizing or sticking, sometimes considerably, to the point that even trying to move the gear by hand does not work.

Depending on the level of hardening or clogging, the 3-way valves may or may not be repaired. Many times the most direct way to resolve 3-way valve problems is to replace them with new parts. However, now we are going to try to repair them.

Two ways to repair the boiler three-way valve

The 3-way valves are very similar to each other, regardless of the brand of the boiler. For this reason, this tutorial will serve you the same way to repair a three-way valve on a Saunier Duval boiler, as well as on a Chaffoteaux, Ferroli, Junkers, Immergas, etc.

1. Check if there are problems in the servo motor of the V3V

It is possible that the three-way valve is malfunctioning for reasons other than itself. For example, it may be that the electronic board is faulty, and that it is responsible for the malfunction of the 3-way valve. We will know this by first checking and ruling out possibilities.

That is why in this initial step to repair the three-way valve of the boiler, the first thing will be to check if the valve servomotor is good or if it has broken down. Beyond the symptoms that we have already seen, which indicated that the 3-way valve could be faulty, the most direct way to find out is by checking the electrical part (the servomotor) of the 3-way valve using a multimeter or multimeter, be it digital or analog.

To check the servo motor, it is best to remove it from the valve but without disconnecting it from the power supply. Once we’ve taken it apart and kept it plugged in, we ask someone to turn on a hot water tap in the house. If when opening a tap the stem of the servo motor moves, it does not have any problems; and if it does not move, it is damaged, or that the current is not reaching it.

05 Detail or close-up of a yellow and black multimeter on black background

Then it is appropriate to disconnect the servomotor and measure with a multimeter if the current reaches it (which must be 220 V). If it does, in fact, it is the servo that is faulty. If it does not arrive, the electronic board is not sending the signal well (it will have to be repaired or replaced), or the cables have problems and must be checked.

If the fault is only in the servomotor and not in the hydraulic part of the 3-way valve, the problem is not so serious. We can purchase the spare part for the servomotor and replace the damaged one. The servomotor has the function of diverting the water to one side or the other as appropriate, and can be damaged by normal use (when it reaches the end of its life time), or when it receives a blow, etc.

By replacing the actuator that works in conjunction with the 3-way valve, if that was the problem, the valve can really be as good as new.

Acquire at Suner the valve servo motors for your business

2. Lubrication to repair the boiler three-way valve

An important part when repairing the three-way valve of the boiler is lubrication. The three-way valve, as we have said, can seize or get stuck in its hydraulic part. Sometimes, before resorting to replacing it, we can either tap the hydraulic part of the valve (this sometimes makes it work perfectly), or disassemble it, open it and lubricate it to restore its mobility.

To repair the three-way valve of the boiler by means of lubrication, the following steps can be put into practice:

  1. Empty the water from the boiler. To remove the 3-way valve, you must first empty the boiler of water, for which you must first close the heating and domestic hot water circuits (inflow and return), as well as unplug the electricity from the boiler. Open the drain valve (do not use the safety valve for this, because it will be damaged) or the drain valve if there is one, and empty all the water content.
  2. Access the 3-way valve. Use the boiler user manual to learn how to remove the front cover of the equipment and access the three-way valve. The position of the 3-way valve will also appear on the boiler diagram in the manual.
  3. Remove the 3-way valve. Now it is time to disassemble the V3V. The first thing is to remove a tab that holds the servo motor or actuator (the electrical part of the valve) to the hydraulic part. By removing the tab, we can now remove the servo motor and put it aside (it is not necessary to disconnect it). Then, using a wrench, we unscrew the 3-way valve counterclockwise until it comes free. Even if we have emptied the boiler of water, there is always some water left, so before removing the valve, it is best to place a container below it to collect the liquid that comes out.
  4. Check if it is better to lubricate or replace. Once we have the valve in hand, we can see that in the centre it has a stem with a spring (which is the mechanism that the servo motor moves to carry out the actions of the valve). In this case, the stem will be stiff, stuck or seized, and for this reason we must proceed to give it some brief maintenance, which will allow us to determine if the lubrication will be sufficient, or if it is best to acquire and install a new 3-way valve. Maintenance consists of activating the mechanism over and over again using an elongated tool. If little by little the mechanism moves, even with work, it will be worth lubricating. If it doesn’t move at all, it’s probably best to replace the valve.
  5. Lubricate the valve stem. If little by little the valve mechanism begins to move, then at the moment the valve is not low, and it is worth lubricating the mechanism. Take some lube (preferably plumbing lube, but if not, use whatever lube you have to hand, even bearing grease), and put it on the stem and mechanism as you move so it spreads well. You should notice that the mechanism becomes smoother and smoother. Be sure to put lubricant on the extreme tip of the stem, which appears when you press the mechanism, and on the thread of the valve and its rubber gasket. Once the stem and mechanism are well lubricated, take a cloth or paper and wipe off any excess lubricant.
  6. Put the 3-way valve in place. Once the valve has been well lubricated and without visible remnants of lubricant, it is time to put it in its place. We perform the reverse procedure, opposite to when we removed it. We screw clockwise, first by hand and then with a wrench. We place the servomotor, the tongue and the external cover of the boiler, and check if the DHW and heating circuits are no longer connected. If so, the job has been perfect.

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