Classic check valve problem?

[Minimia]

Hi there,

I've got what seems to be a common problem - when HW is on, the rads upstairs get hot. Not nice, what with the weather we're having lately!

I've done some research, mainly on here, and it would seem that I'm having a check valve problem.

I've looked at all the pipework in the airing cupboard, and I'm all at sea. I haven't got a clue what's what.

There's a round blue thing that I can identify as a hot water pump. So I don't reckon that's the problem. We've got too much heat, not too little.

There's a Myson Aerject, which is for getting rid of bubbles, I've just learned. That's not going to be the problem, is it?

There is also a silver metal Honeywell box, sitting at the junction of three pipes just off the HW cylinder. It is about 10cm*5cm*5cm, and has a cable running to it. I have no idea what it could be. However, as it's powered, and sitting at the junction of three pipes, just off the HW tank, I'm assuming it's some kind of powered valve. I'm sorry - it doesn't seem to have a part code on it, just some unintelligible specs regarding its voltage etc.
Is this the check valve? Is this the knackered bit?

You'll have noticed that my technical expertise is some way short of crap, so I'm assuming you'll advise me to get a professional in. Is this the thing to do? If so, roughly how much would it cost to get replaced? I'm worried that my ineptitude will mark me out as a target to be ripped off.

Thanks guys.

 

[chrishutt]

Sounds like you've pretty much sussed the problem, Minimia. Not bad for a novice.

The motorised valve (or diverter valve) is not doing what it should be - namely sending all hot water to heat cylinder. May be problem with mot. valve, or with control switches feeding it. To work that out you need to understand the circuit diagram, which is available on honeywell web site (perhaps some kind person will post the link?).

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Ok, I'll do it myself. the link is-

http://content.honeywell.com/uk/homes/Catalogue/Sundial Plans/3.4 Y Plan.pdf

I know that kevplumb does it so much better, so you just click on it, but I haven't worked out how to do that yet.
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moderator

please note 10a

 

[ChrisR]

Well done for describing what you have, if only others...

The problem is not likely to be wiring if it was OK once, though it's just possible the programmer has gone faulty.

More likely it's the valve sticking. It comes apart - the silver head/actuator comes off the brass valve part (assuming there's a small pimple on the head - all in one if not).

You'd probably be charged about £50 for the head or £70-80 for the whole thing (both parts)(actually its hard to get the head separately any cheaper).
Changing the head alone is doable within the first period of charging, but if the whole thing needs changing it could take a lot longer, depending on how things are. It may well be necessary to drain out and refill, either of which may not be simple.

 

[Minimia]

Great replies guys - thanks for that.

So, we're assuming that the silver Honeywell box should be operating a valve, and it's failing to do that. That kinda makes sense, in a theoretical way.

As you say, it seems unlikely the electric control system has died - we're probably talking about a failure of the valve mechanism.

Now, it seems to me that you're saying I should try to free up the sticky valve, by looking for a pimple thing on the valve body, and giving that a twist or some such thing. Fair enough, I'll give that a go. If that frees it up, great. But let's assume it doesn't work.

So, I call a plumber and he comes out, and tries to change the head. He can't. So then he has to try to replace the whole Honeywell box thing. This requires draining the whole system, right? This requires several hours work you're saying? I just don't want to come over as a clueless idiot beggin to be ripped off.

Again, I really appreciate your advice here...

 

[kevplumb]

if there is not a dimple on the motorised head it it NOT removable

well it is but you will get wet

 

[ChrisR]

free up the sticky valve, by looking for a pimple thing on the valve body, and giving that a twist

Didn't say anything like that.

Either the head, or the whole valve, will need replacing.

If for example the valve (brass) bit has leaked into the head to make it stick then you want a whole new assembly.

WHole valve- typically 1-2 hours

 

[Minimia]

That was really helpful guys - thanks a lot.