Hot water only works when central heating turned on too. Why?

[Leo Ismail]

Hey everyone,

I'll keep it short.

Had our old system boiler replaced with a new Ideal system boiler set up.

Then the problems began.
First issue was the pump went faulty, so the pump was replaced.
This then led to a new issue coming up where the central heating would work, but not the hot water, issue was believed to be the motorised valve on the tank.
This has now led to the Ideal boiler showing the FD fault, which according to ideal states there is no water flowing from the main supply to reach the boiler, although I can't understand how that can be the issue if the central heating works fine. Surely the mains water is needed for that so there must be water flowing?

The plumber who changed the motorised valve is saying there is an air lock/air in the system causing the problem, and is quoting us to air vents into the pipework to release it. But....I'm starting to think they're trying to mug us off.

Absolutely nothing online refers to this being the potential cause..... and when I asked why the air in the system only affects the boiler when it's just hot water turned on and not central heating, the response was "Yes, this can occur on both heating and hot water if air gets trapped above the boiler and can't get out" which....is not really an answer to the question.

I just need some honesty, from somebody who's hopefully dealt with this issue before.

WHY does my boiler work fine if i turn on central heating AND hot water at the same time, but if i turn on JUST hot water, it doesn't fire up, baring in mind the boiler, pump and motorised valve on the tank are all new.

 

[Deleted member 120897]

Could be a faulty motorised valve. Yes it could be air, because the hot water feed is diverted to the cylinder coil, so could be trapped there. Air vents should have been fitting when this was replaced, unless of course you refused them to be fitted due to cost? Can you post a photo of the cylinder location and the motorised valve(s)?

 

[king of pipes]

It's standard practice to fit air vents on all high points especially the coil on the cylinder old systems can be problematic for trapping air, you say you have a system boiler now does that mean the small tank in your loft has now been removed? and your system is now sealed ? was the system cleaned either chemically or jet flushed ?? Post a few pictures please.