Heating control question

Dtp1979

2 prog stats and standard flash timer for hot water. I Want the hot water to take priority when either heating zone is activated alongside the hot water.
The reason for this is because the heating operates with weather compensation. But when hw is activated the boiler overrides weather comp and turns up to 82 degrees to heat the cylinder as fast as possible. This is all fine once the HW is timed seperate to heating. But if they come on together the boiler fires at 82 and the rads become scalding hot.
Here's a basic layout. PL and Neutral omitted for clarity
Edit... I want it so that when HW reaches 60 the heating will go back to weather comp mode.

Wearb

I haven't given this a lot of thought, but would a pipe stat on the heating return set at 60 and wired back to the 2 left MV's do the job. Return gets to 60 and they close the MV's.

Dtp1979

Wearb wrote: »

I haven't given this a lot of thought, but would a pipe stat on the heating return set at 60 and wired back to the 2 left MV's do the job. Return gets to 60 and they close the MV's.

What about the weather comp? If it's a hot day heating might only get to 35/36

Wearb

Dtp1979 wrote: »

What about the weather comp? If it's a hot day heating might only get to 35/36

Do you mean that on a hot day the DHW will drive rads above 35/36?

Dtp1979

Wearb wrote: »

Do you mean that on a hot day the DHW will drive rads above 35/36?

Exactly yes, but only if both are on together

Wearb

How does the weather compensator work? Is it controlling a gas flow valve? If yes...does that not interfere with the modulation? If its all done in some complicated way through a pcb, then I don't think know if you will be able to get a feed to control the MV's.

Really what you need is for the weather compensator to control the MV's when the hot water is on. (breaking the link when dhw is off would be easy) Is there a feed from the weather stat that you can pickup. I suppose not, as that is probably just informing the boiler of the outside temp and the boiler is doing the rest. I done really see a way of doing it. Trouble is that its not a specific temperature control, it is a variable control. The operating temperature of the heating system varies as the day varies.

2 Boilers

Dtp1979

Wearb wrote: »

How does the weather compensator work? Is it controlling a gas flow valve? If yes...does that not interfere with the modulation? If its all done in some complicated way through a pcb, then I don't think know if you will be able to get a feed to control the MV's.

Really what you need is for the weather compensator to control the MV's when the hot water is on. (breaking the link when dhw is off would be easy) Is there a feed from the weather stat that you can pickup. I suppose not, as that is probably just informing the boiler of the outside temp and the boiler is doing the rest. I done really see a way of doing it. Trouble is that its not a specific temperature control, it is a variable control. The operating temperature of the heating system varies as the day varies.

2 Boilers

I've no space for 2 boilers
Weather comp is calculated from an outside sensor and the boiler stat goes up and down according to the outdoor temp

Pete67

If you use a 2 or 3 pole relay (8 pin or 11 pin) on the hot water side, you can use one of the spare poles to disable the heating volt free signal when hot water is called for. Just wire a NC contact in series with the heating control signal to the boiler, and heating will be disabled when hot water is called for.

Dtp1979

Pete67 wrote: »

If you use a 2 or 3 pole relay (8 pin or 11 pin) on the hot water side, you can use one of the spare poles to disable the heating volt free signal when hot water is called for. Just wire a NC contact in series with the heating control signal to the boiler, and heating will be disabled when hot water is called for.

Think I got it sorted on the electrical forum. Thanks