CH/HW WITH SINGLE MOTORISED VALVE:

[RONCHAM]

Thanks Dave - don't be hard on yourself, I had the benefit of looking it up before I replied to you!!

Thanks D_Hailsham too - I know you're giving me good and safe advice. If you saw my intro I've got TRVs on all rads (think bathroom rad is a bypass too) AND on HW tank (via copper wire sensor on tank). So only control is boiler stat or when programme ends. Even so I've never had HW extremely hot (after say 2 hours) - perhaps becos it's got 15mm inlet which may be smaller than the norm(22mm?). Pipework is convoluted (and wiring!) plus a lack of space which is why I'm reluctant to fit another MV or single 3-port MV. Would like a slimline tank but they're big bucks.
I upgraded old Switchmaster programmer to a Lifestyle LP522 which I'm pretty sure can handle the arrangement you suggest
Regards,Ron.

 

[D_Hailsham]

If you saw my intro I've got TRVs on all rads (think bathroom rad is a bypass too) AND on HW tank (via copper wire sensor on tank).

Yes, I had read that before I replied.

Even so I've never had HW extremely hot (after say 2 hours) - perhaps becos it's got 15mm inlet which may be smaller than the norm(22mm?).

Apart from the thermostatic valve in the HW cylinder circuit, is there a second valve, say in the return? If so, this could be closed down so the cylinder does not get more than its fair share of the heat.

Pipework is convoluted (and wiring!) plus a lack of space which is why I'm reluctant to fit another MV or single 3-port MV.

Understood, I was only pointing out the pitfalls.

If you can post a photo of the cupboard showing the general layout, someone may be able to suggest a solution.

The LP522 will allow setting of separate heating and hot water times.

 

[RONCHAM]

Yes, I appreciate you were looking after me! - and thanks again.

I know it wouldn't be impossible to install a 2nd MV or 3-port MV even in the space I have but it would be a lot of plumbing to rationalise the pipework. So I was looking for the "soft" option without compromising safety. Not actually happy with present arrangement whereby boiler stat turns off boiler/pump unless programme ends. There is an in-line cheap and nasty service valve in return from HW tank but this is presumably just for isolation purposes.

 

[D_Hailsham]

I know it wouldn't be impossible to install a 2nd MV or 3-port MV even in the space I have but it would be a lot of plumbing to rationalise the pipework. So I was looking for the "soft" option without compromising safety.

It's your call.

Not actually happy with present arrangement whereby boiler stat turns off boiler/pump unless programme ends.

The room thermostat should be controlling the opening and closing of the MV and the boiler should be controlled by the auxiliary switch within the MV. So, when the roomstat shuts the valve, the boiler automatically goes off.

There is an in-line cheap and nasty service valve in return from HW tank but this is presumably just for isolation purposes.

If it's not a full bore valve it will be restricting the flow.

Two-hour cylinder heat up is long. Do you have a foam insulated tank or just one of the red loose jackets round it?

 

[RONCHAM]

Of course there isn't a room stat at present! - which is where I came in!! Thought I could install one and set it "lowish" with room TRV set high or disabled. think that valve is full-bore type - it's one of those £2 cheapos (cannonball?) you open/shut with a screwdriver and I've never dared to touch it!

 

[gas4you]

You probably have an imitation ball-o-fix valve. If so these are far from full bore, probably only about 6mm when open fully.

 

[D_Hailsham]

Of course there isn't a room stat at present! - which is where I came in!!

Overlooked that fact.

Thought I could install one and set it "lowish" with room TRV set high or disabled.

You could do that, though I'm not sure what you mean by 'set the room stat "lowish"'. You normally set a room stat to the temperature you want the room to be, 20°C is typical.

Your system is, to put it mildly, very basic, with no proper control over room or hot water temperature, relying on a time clock, the boiler thermostat and TRVs on the rads. The amount of money being wasted on gas each year would probably pay for any upgrade within a year or less.

You need to think seriously about this, bite the bullet, and get your system upgraded over the summer.

 

[RONCHAM]

Thanks D_Hailsham - didn't see your final comment. Btw, there is a TRV on the HW too. Yet this arrangement with a single MV seems very common - not sure why as it would be fairly fairly cheap and easy to add a 2nd MV at same time (or a diverter). The folk who had this installed weren't short of a few bob either - perhaps the plumber did it more for HIS ease and convenience??

Your conclusion is absolutely right of course (trouble is, a new and more efficient boiler would be a good thing too which puts it in the realms of £2-3K (more like £4K with BG!). I'd rather move house!!