No hot water or no heating!

[alison7148]

Earlier this winter we had a problem with our ystem when we had hot water, but no heating - I couldonly get both by movingnthe mid-position valve manually. This seemed to resolve spontaneously after a couple of days so we didn't get anyone to look at it.

Last night we had both heating and hot water, but the heating would not turn off despite turning the thermostat down. Today we have had heating but no hot water. I have turned the heating off on the programmer and left the HW on but the radiator stay hot and the water is still cold. I am guessing it is probably a new mid-position valve that we need, btu we only had it replaced about 4 years ago. Do they generally have a short life-span? Or could it be something else?

Any suggestions before we call the gas engineer?

 

[John506]

You need a new 3 port, if you have manually left it open then you will get circulation around your CH regardless of it being on or off.

You can also get these problems with badly planned out pipework and if ignoring the 3 tee rule, but as you speak as though it has only just started after manually opening the 3 port, sounds like the above

 

[alison7148]

I have tried turning everything off and then just the hot water on (without the heating) and I think the water is gradually heating up now. The valve is now back in the automatic positiion ( i haven't left it on) so maybe i will just wait and see what happens in the morning?! We live in a very 'hard water' area, so wonder wheher that has clogged up the valve or whether it is a simple mechanical failure. Its driving me mad that I don't really understand howthese things work!!

 

[John506]

3 port valve has 3 ports.

A - Central heating
B - Domestic hot water
AB - Flow from boiler.

There is a ball in the middle of these ports, if you choose to have CH on, but don't wish to have hot water from your tap, the ball will move and cover the B side, so the water can flow from AB to A.

If you wish to have hot water from the tap but CH off, it will move and cover the A side, so water can go from AB to B.

The reason it is called a "mid position" is because the ball can also sit in the centre of the valve, letting water from AB into both A and B, so you can have Central heating on and get hot water at the same time.

The other version called a diverter valve, cannot sit in the "mid position" to supply both, only one at a time.

Your domestic will have priority though, so if you turn your CH on and run a hot tap, your CH won't heat up until you turn the tap off. But this doesn't apply to you as you have a mid position and it can supply both.

It is possible it could have scaled up, not an uncommon problem for the motor in these to go though, probably a more likely if it still operates manually.

 

[Hugh Jaleak]

Hard water wont make any odds, the heating system should circulate the same water (unless its drained for maintenance). More likely either sludge in the system or certain makes of valves dont seem to manage above 3-4 years before failing... Sunvic valves have a habit of playing up, soon swapped mine for a Honeywell, they're a few £ more but have a better reputation.

If you're really keen to know how the valve works there is a good technical explanation by D.Hailsham in the Boiler and Central Heating FAQ's on page 2.

 

[alison7148]

Thanks - that makes a bit more sense now! xx