Boiler not turning off - Honeywell V4073A valve problem

[Tykey]

Ah, ok. That kind of makes sense.

The boiler is a Main System 18 HE.

I've also traced back the five pipes that run from the loft to the airing cupboard, and from left to right they are:

1) Hot water to pumped shower processor box in loft
2) Even though it's got a red tap and "H" written on it, it's the cold feed from loft tank into the back of the water cylinder at the bottom.
3) Cold feed from loft tank, straight through the floor. Don't know where this goes, but thought it would be the boiler.
4) Expansion pipe to loft tank
5) Mains to loft tank

View media item 100875

 

[terryplumb]

The expansion vessel is within the boiler. Think there is a pressure gauge on the boiler ,as well as the one in cupboard for convenience when using the filling loop. Your pics a bit fuzzy , but the gauge appears to be 0 pressure ??

 

[Tykey]

Yes, thats correct. There are two pressure guages

The system is completely cold, and it's showing as 0.5bar on the boiler guage and pretty much zero on the one on the filling loop. Very strange. Either way it's going to need a top-up.

In terms of draining it down to replace the valve (which is what caused all this hassle in the first place) how would this part gravity, part sealed affect that?

Presumably I can just cut off the feeds from the loft tank, then drain off at the drain valve on the bottom-most radiator until it's at below the level of the 3 way valve?

 

[terryplumb]

As the cold water from loft tank and hot water cylinder do not mix with the sealed system water you don't need to touch anything on the gravity set up. Just make sure the filling loop is fully closed , open drain cock at lowest point ( hose pipe to a drain ), open air bleed valves on upstairs rads to break the vaccum and allow air in. Firstly isolate electric supply ,and prove dead , to boiler / all components. Before filling system up add inhibitor and check all bleed valves are closed.

 

[Tykey]

Brilliant, thanks a lot for your time Terry. I will give that a go.

 

[Tykey]

Sorry, me again!

I drained the system - brilliant!
Changed over the three-way valve - wonderful!
Refilled the system; no leaks - fabulous!
Bled all the rads from bottom to top, refilled to 1bar, turned on the boiler and tested it with different CH and HW functions selected; all working fine - hurrah!

However...

A couple of hours later, the boiler started making a racket, and when I went to look at it, a fault indicator was flashing - Low pressure or pump fault. Pressure showing at 1.5bar (as the system was now hot) so it's not low pressure, so must be a pump issue.

I went around the house re-bleeding, and got a little more air out. I also undid the screw on the boiler pump, but water came out immediately rather than air.

Anyone got any suggestions for what I can take a look at next? Or is it a case of leave it a couple more hours, re-bleed, and continue until all the air is out?

Many thanks in advance.

 

[Tykey]

I've been going around re-bleeding then topping up, and for the time being it seems to have done the trick.

The pump is back to its normal sound levels, and the fault indicator is no longer showing. I'll keep on top of any more air on the system over the next few days and hopefully that should sort it.

 

[Tykey]

HELP!

After replacing the three way valve, it seems as though I am back to square one. I enjoyed fully-functioning CH and HW for a whole evening last night, but waking up this morning I found that the original problem is still there.

Here are my current symptoms:

1) When the boiler (Main System 18 HE), progrmmer and motorised valve are on at the isolation switch, the motorised valve offers no resistance when moving from auto to manual. When power is cut via the switch, the valve arm returns to its default position.
2) When the boiler first turns on from cold, it tries to fire up three times and fails. When it fails to light, if you reset it, then it lights normally first time.
3) When the boiler is turned on, there is a permanent demand on the boiler, irrespective of whether the programmer is calling for heat or not.

Can anyone offer any further suggestions please?

 

[Terry lambert]

Where is your boiler located

 

[Tykey]

Hi Terry. The boiler is in the kitchen, directly below the hot water cylinder that is in the airing cupboard (in the bathroom) upstairs.

 

[Terry lambert]

Your boiler failing to ignite and your boiler firing with no demand are selerate problems, I would call an engineer as you would need him to identify the ignition issue and it shouldn’t take him long at all to trace with a multimeter what is sending a demand to your boiler

Sometimes DIY isnt the way to go

 

[Tykey]

Thanks Terry, I came to the same conclusion this morning so I have someone coming out to me tomorrow morning. On the phone he said it sounds like it would be two separate issues too, so I'm glad you're both in agreement there.

I'm a keen DIYer and always looking to expand my knowledge, but I recognise where my limits are (anything more than entry-level electrics is one of them!) and have bitten the bullet to get an expert in.

I'll report back with what he finds on the off chance it might help someone in future if they come across this thread.

 

[Tykey]

Just to finish off this thread in case anyone else comes up against the same problem.

I had a heating engineer to come in and have a look at it, and after he looked over all the wiring and checked the room stat and cylinder stat, he declared it to all be wired up and working fine. However, there was still a very small amount of current coming to the boiler from the valve, which was enough for it to be constantly demanding heat. He called honeywell, and it must be a known issue, as their immediate response upon hearing the issue was "You need a suppressor. We have a whole drawer of them, we'll send you one out free of charge." It arrived next day, he fitted it, and hey presto, no more demand for heat.

As for the boiler firing up issue, this was down to the electrodes. He replaced the defective ignition electrode and flame rectification probe, and it now fires up first time, every time.

Back to a fully working system, and in the process I've learnt a lot about my own heating system setup and how the 3-way honeywell valve works - a clever bit of kit.

 

[shambolic]

Some boilers will fire up with a small back feed of voltage from the 3 port valve.
We used to fit a suppressor to ours to stop this too.