Mystery boiler....

[Ricky999]

Hi, my boiler has recently started misbehaving. I can't figure it out, hence posting the symptoms to see if anyone can shed any light! It's a Valliant, located in the kitchen, and it's closed system with a water tank upstairs. Controlled by Hive and about 20 years old, but been serviced every year. I am currently using the Hive schedule for hot water and heating is turned off. The problem is, the boiler is not firing for hot water at the scheduled time, even though Hive says it's on. There are no error codes on the boiler.

If I then turn the heating on, the boiler fires and also heats the water. If I turn the heating off immediately, the boiler also turns off. If I leave the heating on for 15 minutes, I can turn the heating off, but the boiler still fires, to heat the water per the schedule.

I've also observed; if I turn the boiler power off and Hive hot water schedule off. Then turn the power back on, and then hot water on via Hive, the boiler will fire. No need to engage the heating.

I assume it's a control problem somewhere in the boiler? Any thoughts or tips are appreciated, either to resolve it, or please let me know if you think it's risky carrying on with it into winter. Obviously the heating will be on in the winter, so it will be easier to manage?

thank you!

 

[Harry Bloomfield]

and it's closed system with a water tank upstairs.

I think you may mean an 'open vented system' - A tank storing cold water, which fills a cylinder, likely in an airing cupboard?

If I then turn the heating on, the boiler fires and also heats the water. If I turn the heating off immediately, the boiler also turns off. If I leave the heating on for 15 minutes, I can turn the heating off, but the boiler still fires, to heat the water per the schedule.

If an open vented system, you may have either an electrically operated valve, with three ports/pipes entering it, or two electrically operated two port/two pipe valves.

Your post suggests that one, or other of these has perhaps failed, or stuck, not fully opened enough to trigger it's microswitch.

 

[JohnD]

Look for one or more of these

IME they are usually Honeywell or Drayton, and can last around 15-20 years

https://www.screwfix.com/search?search=Port+valve&category=cat830966

P.s.

They way they work, in the most common 3-port valve, the timer and the cylinder stat send a signal to the motor that turns the valve. There is a switch inside the motor casing. When the motor gear reaches the end of its travel, it switches on the boiler. The motor also drives the valve to a heating position, and at the end of its travel, switches on the boiler.

If the motor was not switching on the boiler reliably, if would be consistent with the fault you describe.

It is possible to change either the motor part or the valve part, but if your assembly is 20 years old, you probably need to change the whole thing. It is a moving part and wears out.

 

[Ricky999]

I think you may mean an 'open vented system' - A tank storing cold water, which fills a cylinder, likely in an airing cupboard?



If an open vented system, you may have either an electrically operated valve, with three ports/pipes entering it, or two electrically operated two port/two pipe valves.

Your post suggests that one, or other of these has perhaps failed, or stuck, not fully opened enough to trigger it's microswitch.

Thanks Harry! TBF, I am not sure if I have the terminology right. There is a tank in the airing cupboard, but it's sealed. But there isn't an open tank in the loft. It's just a boiler and tank. I will have a look at the valve!

 

[Ricky999]

Look for one or more of these

IME they are usually Honeywell or Drayton, and can last around 15-20 years

https://www.screwfix.com/search?search=Port+valve&category=cat830966

P.s.

They way they work, in the most common 3-port valve, the timer and the cylinder stat send a signal to the motor that turns the valve. There is a switch inside the motor casing. When the motor gear reaches the end of its travel, it switches on the boiler. The motor also drives the valve to a heating position, and at the end of its travel, switches on the boiler.

If the motor was not switching on the boiler reliably, if would be consistent with the fault you describe.

It is possible to change either the motor part or the valve part, but if your assembly is 20 years old, you probably need to change the whole thing. It is a moving part and wears out.

Thanks John, I apprecite the info. I will look at replacing

 

[Madrab]

@Ricky999 , from your description, if there are no cold water cisterns (CWSC) in the loft either large or small then it sound like you have a sealed CH system with a HW cylinder. Depending on the type of HW cylinder you have determines whether that may be a combination cylinder (open vent) or an unvented cylinder.
As far as your issue is concerned, you may have either one of these a 3 port valve - Or 2 of these 2 port valve

How they actually switch is quite different but essentially - there is a call for either HW or CH from the programmer - the valve moves to the appropriate port to open the flow to either or, internally there is a switch and when the valve opens that switch closes and sends power to the boiler to turn it on.
From what you suggest is happening It sounds like you have 2x2 port valves (probably on the pipework where the HW cylinder lives), when the HW is calling the HW valve is opening but it's not sending that power to the boiler, that'll be why when you turn on the CH, its valve then opens and it's switch does turn on the boiler and as the HW valve is already open, when the boiler runs the HW heats up. The power cycling may be forcing the dodgy HW micro switch to activate

In short the HW valve is probably faulty and at least the head on it needs replaced but get a recommended engineer in to check and test it to confirm that's what the problem is.

 

[Ricky999]

@Ricky999 , from your description, if there are no cold water cisterns (CWSC) in the loft either large or small then it sound like you have a sealed CH system with a HW cylinder. Depending on the type of HW cylinder you have determines whether that may be a combination cylinder (open vent) or an unvented cylinder.
As far as your issue is concerned, you may have either one of theseView attachment 356223 a 3 port valve - Or 2 of these View attachment 356224 2 port valve

How they actually switch is quite different but essentially - there is a call for either HW or CH from the programmer - the valve moves to the appropriate port to open the flow to either or, internally there is a switch and when the valve opens that switch closes and sends power to the boiler to turn it on.
From what you suggest is happening It sounds like you have 2x2 port valves (probably on the pipework where the HW cylinder lives), when the HW is calling the HW valve is opening but it's not sending that power to the boiler, that'll be why when you turn on the CH, its valve then opens and it's switch does turn on the boiler and as the HW valve is already open, when the boiler runs the HW heats up. The power cycling may be forcing the dodgy HW micro switch to activate

In short the HW valve is probably faulty and at least the head on it needs replaced but get a recommended engineer in to check and test it to confirm that's what the problem is.

Thanks Rob, I appreciate the detailed description. You are spot on, 2 of the 2 port valves. I feel a lot more confident getting it sorted now! cheers, Richard