Central Heating Problems

[Amos]

Hi everyone. First post, but one name I recognise...

I have had the great {srcsm} experience of having our Edinburgh tenement living room back boiler replaced by a condensing boiler off the kitchen. They seemed (at first glance) to manage the gas and pumbing fine. It took the three visits to sort out the electrics, and ended up with me telling them what wires to put where...

Next problem is:

The system is a two independent valve system, and a pump in the boiler. The boiler is permanent mains, so the pump doesn't cut out until a while after the boiler presumably for cooling reasons? I guess that is standard. Inevitably a bypass is needed as both valves (or even all the radiators) can be off. They seem to have put the bypass as close to the boiler as possible, which I can't say flls me with joy as there is hardly a lot of room for circulation.

Anyhow the issue is that is appears that even when the (say) central heating valve is open, I am getting some flow through the bypass which has what I presume is, from Ed's decription, a gate valve. the result is that the return to the boiler is hotter than it should be.

My questions are

1) Is this right? I am presuming I should get no flow through the bypass if one or other valve is open and the radiators are on? 2) What is a gate valve precisely, and how does it work? 3) Is there some way I can solve this problem? 4) Is there anything the fitters should have done/do.

Gate valves seem to be something every google hit wants to sell me, and none wants to tell me about :)

Thanks!

Amos

[Ed Sirett]

A gate valve is a simple metal plate that slides into and out of the pipe.

They are not very good at completely sealing the flow. They offer little resistance to the flow when fully open. The don't corrode when half open like some 1/4 turn valves, which is what it likely is set to hear.

They have been surpassed by 1/4 turn stop valves for use in plumbing.

1) Maybe, depends on the boiler instructions. A smart bypass would off little or no flow until needed. 2) See above 3) It may take some experimenting to get the best setting for the bypass. Or it may require replacing with a smart bypass valve. 4) Depends on the boiler instructions - which may specify a minimum length for the bypass circuit.

[Set Square]

A gate valve is just a manually adjustable tap, which offers less flow resistance than an ordinary tap when fully open.

In order to act as a by-pass, the gate valve would need to be partially open - so there *will* be some flow through it even when the CH and/or HW circuits are open.

It's far better to use an automatic by-pass valve (referred to by Ed as 'smart') which is spring-loaded and only opens when the flow has nowhere else to go.

[Dave Plowman (News)]

A tap screws a 'flat' washer of some sort up against a 'flat' seat - and assuming both of these are in reasonable condition will shut off fully. A gate valve relies on an accurate match between the gate and body - which wear or debris soon spoils, so rarely work as a stop c*ck properly after some service.

[Amos]

Thanks everyone. It is possible it might not be a gate valve then. I guess it may be an automatic by-pass valve, but I know little about recognising these things (give me wires or bits of wood anyday!). I probably better work it out.

In the meantime ;), the said valve is adjustable at the top. Ignoring the obvious damage I could do to the boiler by cutting of the bypass, is there likely to be any damage I could do to the valve by messing about with this. Are spring loaded valves generally adjustable as to how much pressure differential is needed to open them?

Thanks again for your help.

Amos

[John Rumm]

Some piccies might help:

Gate valve:

valve:-

In the meantime ;), the said valve is adjustable at the top. Ignoring

Unlikely to do much mischief to the valve unless you take a large spanner to it!

Often, yes.

[Set Square]

A gate valves looks like

?_dyncharset=UTF-8&q=16874&x=6&y=11&n=&pn=1&pd=1&pi=1&cn=1&cd=1and an automatic by-pass valve should look something like ?_dyncharset=UTF-8&q=67854&x=11&y=12&n=&pn=1&pd=1&pi=1&cn=1&cd=1> In the meantime ;), the said valve is adjustable at the top. Ignoring

Yes, they are adjustable. I don't know whether there's a recognised methodology for adjusting them, or whether it's just suck-it-and-see.

I've never owned one, but others may well come in with some advice.