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.