Mid position valve help

[Elliotnotaplumber]

Hi all,

I am newly registered. This forum has been a useful resource since buying my own house 9 months ago - so thank you to everyone that contributes.

Far from an expert DIYer and certainly not a plumber, I am fairly mechanically minded and comfortable with most tools, so lately have been tackling an annoying problem with our heating system.

The symptoms aren't anything new: when our hot water is on, the radiators upstairs come on too.

Obvious starting point was the mid position valve. I duly drained the system down and removed it, before replacing with a Drayton MA1, like for like - NO CHANGE.

I double checked the orientation and wiring, before admitting I didn't know what to do next. So I called in a plumber (who is a friend), who turned up with an electrician in toe (they are part of a bigger firm).

Immediately he diagnosed the problem to be the mid position valve installed back-to-front. Great thought I, so I drained down and reversed it...same problem.

I got the plumber back, who tested the new valve i fitted (fresh from screwfix) and said it was faulty. They fitted a new valve from the van whilst I was at work and called to say problem solved...except, when I got home the upstairs was roasting even though only hot water was on...either they didn't stay long enough to verify or the problem came back.

Can anyone offer any obvious insights? Things that I should have already checked?

To give some background:

System is gravity fed with a small tank in the loft with a ball & cock setup.
Boiler downstairs is an ageing glowworm (which actually is a trooper and was serviced last year)
I only have 5 rads in the whole house (small terrace)
When heating is on, all rads get nice and hot (system has been drained and inhibited 3 times in one week!)
Pump is 'wurring' and does not rattle etc
Hot water comes through fine.
I have a Drayton Thermostat (pictures) which is currently showing green status and works ok.

I have attached some images currently on my phone.

 

[stem]

Hi Elliot and welcome to the forum.

In this instance, my first suspect would not have been the motorised valve itself, unless the valve is physically stuck open. This is unlikely when you have replaced it, to have another one in the same condition.

The valve when un-powered, sits at rest in the 'hot water' only position. When power is applied to the valve motor it winds it to the heating position. So it would appear that power is being applied to the valve motor from the controls.

Has the system ever worked properly or has it always been like this?
Have you altered anything else during your fault finding?
If the fault has just occurred, did anything else happen or was any other work on the heating system or to the property done around the same time time that might have had an effect?

 

[Elliotnotaplumber]

I moved in after winter last year so this is the first time I have personally used the heating. I did notice over the summer that some of the rads were getting some warmth in them and simply used the TRV's to sort the issue as a stop gap (probably should have sorted it then!).

During fault finding I have added inhibitor and free'd up some of the TRV's. I did also put new batteries in the thermostat control which took away the red light on the digisat box in the airing cupboard. I do not really use the thermostat - I just run the heating on timer in the morning and night.

All 3 valves I have had on the system have moved. I don't recall if the 1st was functioning incorrectly, as I thought £50 to replace it was a no-brainer given the symptoms. The new valve I fitted and the plumbers ones have moved to the correct position, relative to the controls, as described by you above.

For clarity, each time the 3 way has been replaced, it has been with a complete replacement (actuator, valve, motor).

 

[stem]

Sounds more like a problem with the controls to me, it may not even be wired up properly. Unfortunately, the only way to be sure for certain is to check the wiring through with appropriate test gear, but you would need to be electrically competent and understand circuits to be able to do this.

One simple test you could try, if you can do it safely, is to disconnect the motorised valves white wire, and then operate the hot water. If the upstairs radiators don't heat up now it is a problem with the wiring or the controls and not the motorised valve.

Or, it may even be that the upstairs radiators are getting reverse circulation because of bad plumbing, or aren't even plumbed through the aforesaid motorised valve at all! Stranger things have happened.

 

[Elliotnotaplumber]

I can isolate the white wire relatively easily as a helpful person at some point put a plug between the motor and the controls.

Will try this and see where I get to.

I had thought about reverse circulation or at worst no circulation through the valve, but need to exhaust other options.

Really, I don't want to get the plumber back a third time...its beginning to grate only paying for diagnostics and no solution at the end.

 

[stem]

Putting a plug to the motor is not straight forward and may confuse matters as the valve also gets power from a 'hot water not required' signal from the programmer and cylinder thermostat on its grey wire.

Anyway, lets see what happens when the white wire is removed. That's the heating 'on' signal from the controls that tells the motorised valve to move the central heating position. When you do the test and put the hot water on, the hot water cylinder should be cool and requiring heat, otherwise nothing at all will happen. The boiler needs to actually run and the hot water system be working for the test to be meaningful.

 

[Elliotnotaplumber]

Image 0248 shows the plug. It's just an in-line connector so that the box doesn't have to be popped open each time in order to wire up the motor - its just a bit neater, that's all.

Thank you for your help thus far.

 

[stem]

Thanks, I suspected that, the wire colours gave it away. Nice idea, makes swapping the valve easier.