LP 722 Programmer modification

Hello
I have an LP 722 programmer......unfortunately my heating system has a problem......the boiler doesn’t like it when heating hot water only..had great difficulty controlling the temperature, often cuts out iron over temperature, maybe it’s a piping configuration issue, I don't know.

But my idea is, to have a setup, where the hot water will only Run if the heating is in demand, but this would only be for the Winter months, during the Summer, I have no choice but to let the boiler heat hot water only, but my plan is to reduce the KW down from 18 to maybe even the minimum of 4KW.

Is there any way of introducing a switch ( possibly 2 way ) which in one position would achieve disabling hot water if the heating is not in demand.

Many thanks

The LP 722 programmer has Line for clock, and both Coms internally linked. So rewiring is limited, however can't see a problem in a switch between the two N/O contacts and set the domestic hot water off, and then it would only work with the central heating.

However the cure is to repair the boiler. I would try turning down the temperature of the water first, but the idea with any central heating with a modulating boiler is the TRV heads control temperature, as they close the by-pass valve will lift, and the return water temperature increases, and boiler modulates until at minimum, at which point it uses a mark/space ratio, so can't see how combining DHW with CH will help.

The Hot water circuit is very small. ( short ).....the boiler runs ok if the immersion cylinder is fairly cool, but if still reasonably hot, the boiler just can’t cope, fires up and immediately trips on high temperature, already I set Hot water only 3 times a day for an hour or so to avoid this, would love it on constant.......the OLD boiler a potterton netaheat had the hot water on a thermos yo hon, from memory, the new ( 8 years old ) Vaillant ecotec 418 is a fully pumped system, but heat only, the separate hot water option was not fitted.

thanks

It might not be as straightforward as you think.

If there is a room thermostat and hot water cylinder thermostat fitted, once the programmer has switched them on, they are responsible for starting and stopping the heating and hot water systems, and the programmer doesn't have any control of this, or know their status. So you could have the situation where the room thermostat switches the CH off, but as afar as the programmer knows it is still on, so would continue to energise the HW.

Also, if you have a 3-Port motorised valve fitted, its working depends upon the single HW contact toggling between on / off. If the CH contact is being used to power the HW, then you run the risk of both HW on & off both being energised simultaneously.

The best solution would be to get the mechanics of the system sorted so that you don't need the modification.

Agreed, my idea is not sound......will work on fixing the problem

thanks for your help...

Your problem is nothing to do with the programmer, make sure your boiler has a permanent live and if S plan that you have a by-pass fitted

Just spoke to Rochester technical ( vaillant ) they have given me the reset to factory procedure, think this could be a good way to go. When the boiler was fitted, the installer, didn’t care that there wasn’t a permanent live for the boiler ‘ run on timer ‘ & as it was gurgling like hell & kept tripping out, I paid an electrician to install a live feed. Some settings may have been changed by the installer as he kept fiddling with settings, but then just went and left me with a boiler that wasn’t really working.

that was 8 years ago and it’s never performed very well....it really can’t manage hot water on its own, unless the immersion cylinder temperature is fairly low, just fires & trips etc etc etc, until eventually the cylinder stat is satisfied.....heating on its own is mostly good, but when hot water & heating are on together it seems to take a while to settle, which doesn’t really make sense.....my thoughts were that either it’s boiler settings....which I am unaware of, or the way the piping was done, my builder was also not as good as I would have liked, maybe the hot water return is causing turbulence where it joins the heating return, no idea, as it’s under the floorboards somewhere.....( as a side story, my builder completely messed up the electrical consumer unit, had to pay another electrician to sort it out, who said it had not been done to regulations, he had omitted the trip cables as he couldn’t get it to work )..in my builders defence, he did say to me, during the install, which was very problematic, “ I am not an electrician “......have to ask why the hell he was doing it then.

so back to my ecotec 418, is a factory reset a good idea, maybe some changes the installer made are causing my problems

thanks

you can only try, do you know if you have a by-pass fitted what is your system is it Y plan or S plan ? post some pics of what you have

No bypass.....is this picture enough ?

Yes you have a Y plan system so no by-pass required, the Valliant 4 series seem to have this problem, possibly @sbgasman could advise you to what to set the boiler to, I have heard of the settings being quite crucial on these but he is the expert

Thanks , would love to ask his advice, bit can’t access his profile, how can I contact him please ? Thanks

calibra said:

Thanks , would love to ask his advice, bit can’t access his profile, how can I contact him please ? Thanks

Click to expand...

I have tagged him in my last message so when he logs on he will see that I tagged him for you

Thank you

sorry see hardly any of these on my patch , you might have a restriction on your HW primary , I usually find these close to the coil return connection at the cylinder .

Thanks, but without a flow meter, it’s difficult to determine ?
Valiant suggest I do a factory restore, do you think this will do any harm ?