wet UFH - no 2-port valve - how does ST699 programmer work with room thermostats?

[lad33]

Hi, hoping for a little guidance please.

I've an electric boiler, so obv with prices as they are looking to run things more efficiently coming up to winter here in the UK.

My programmer/timer is an old Honeywell ST699 (which ideally I'd look to replace in due course because I find it rather inflexible).

Looking at my plumbing, there's no 2-port valve coming off of the flow from the boiler to the UFH.

The actuators on the manifold open, per request from the independent room thermostats. And these remain open, regardless of whether the ST699 is on for CH or not, if the thermostats are set to a temp higher than room temp.

That's as I've observed everything so far.

However, the last few days I've noticed the hot water not being as hot from the taps.

The only thing I can think of that's changed is that I was experimenting with getting the thermostats set for the rooms as winter approaches, and therefore the actuators for those UFH zones are open. Before now, the rooom thermostats (old Rehau dial thermostats have been set to the * position - the lowest on the dial).

SO, at present I am NOT using the CH timer on the ST699 to request underfloor heating.

As there's no 2-port on the flow to the UFH, does that:-

a) mean I'm not on a proper S plan etc. ?
b) mean that hot water is flowing through the UFH circuit regardless of whether or not the programmer is calling for CH, IF the one or all of the actuators are in the open position?
c) that because the actuators are open the larger heating circuit is reducing the heat exchange flowing to the HW storage cylinder in the time allowed by the programmer?

In other words, with no 2-port present on the UFH side of the system to close it off, is the HW side of the system being hindered?

I've seen videos where when explaining Y plan configs the narrator has suggested that CH be set on the timer to a period separate to the HW so as to maximise the heat to one system or the other, so I'm just clutching at the idea that maybe the way my CHS has been plumbed in isn't as efficient as it could be.

Tomorrow, I'm going to turn all the room thermostats back down, so all the actuators are closed again, and after the HW has been on just touch test the flow of hot water to guage it's temp.

However, aside from that, I'm really wondering if longer-term I ought to have a 2-port valve present, and ought to start saving to get a plumber out in the new year.

Thanks for any pointers.

 

[Madrab]

Given your setup, each thermostat connected to the UFH manifold is a zone, the actuators will be controlled by each stat, which either powers the actuators directly or there is an UFH controller. When the programmer calls for CH or HW, then the boiler fires up and the pump kicks in, sending heated water (HW) around the system. Do you have any rads or is it all UFH?

No it's not an S plan - an S plan is where there are 2x2 port valves, one for CH & one for Hot Water. If there is no valve controlling the UFH/CH then it won't matter whether CH or Hot Water is being called for by the programmer, either or will start the boiler and pump and run HW around a single circuit. If the UFH is taking all the flow before it get to the cylinder then there isn't enough flow to provide the cylinder with enough hot water, so it won't work effectively.

To ensure enough HW, you should be able to isolate each circuit by the way of a 2 port valve so each, or both can be selected independently.

 

[lad33]

HI @Madrab, thanks for getting back to me and helping to clarify my thoughts, and confirm my findings that it is not S plan.

Nope, no rads. Just the UFH. I barely use it, but just took the time this week to get some HW running through each zone for annual test before the winter weeks arrive, and then noted the temp loss on the HW even after shutting off CH on the timer during the days following.

I suspect the UFH is taking the flow as you described it when the actuators are open, so I'll test that theory in the coming days, as seems for now, if I want HW only day to day, in order to minimise the time the boiler is on, I need to ensure the thermostats are turned down in each room.

Thanks again.

 

[Agile]

UFH takes a time to heat up a room, often 1-2 two hours. Equally it takes a long time to cool down so heating times are important to obtain maximum economy.

The ideal is to have the boiler heating the HW at times when the UFH is not needed to be on. Some off peak electricity tariffs are still available in some areas and with some suppliers. These could give a saving to enable you to heat water during the night time.

If your UFH zone valves are powered open then all you need to do to turn it off at times is to arrange to depower it. In this case a two port valve is not needed.

Depending on the boiler power the cylinder will probably get reheated in about an hour if the UFH is off during this time.

Once the UFH had warmed the rooms up then it can usually be turned off for half an hour to reheat the water quickly.

 

[Jim1138]

Hi @Agile, thanks for your reply, very helpful and informative.

Yep, takes around 1.5 hrs to start to feel the warmth on the floor, from a cold start (i.e. not previously heated in last 24 hours). I don't generally have the CH on, can't afford to.

I've a budget of 1hr hot water max. per day. That's all 2 people need for showers and pot washing at tea time. The electric boiler uses ~ 9kWh of electricity per hour so it's not exactly cheap for my budget. Actually my budget is 1hr of boiler use per day, it's up to me to figure how to balance our cleaning use with our warming needs in due course.

So, tinkering I'd gotten the boiler usage down to about 40 mins per day, which seems to be enough daily to heat the storage cylinder up for our needs, and I'd wondered which 40 min period in the day was best; either tea-time for immediate shower use, or in the morning, to be able to quickly wash breakfast pots or any from the previous night etc. and still have residual heat by the end of day for showers. I even tried a 20 min split for morning and evening but that just doesn't seem to generate any real useful heat, which I kind of expected to be the case so is a waste of the 40 mins of budgeted time.

It is only after having the CH on for one of the days to check how long it took to feel warmth (and to check that the zones did actually warm) that I noticed the lack of heat to the HW from the taps when using my 40 mins of boiler being on for HW plan. I left the programmer on and could tell after 1h40 mins that the cylinder was still calling for heat from the boiler, whereas before the boiler would shut off around the 45 to 55 min mark.

The only thing that has changed between those days is that I'd left the thermostats at their settings ready to be used when the programmer would be finally switched on for certain time periods for CH, and thus had noted that the actuators on the manifold for those zones were still raised.

I'd not expected the actuators to open regardless of whether the programmer was on for CH. I naively assumed if the programmer triggered CH, then the actuators would be called to open from there, depending on each of the room thermostats present settings at that time.

That's why I'm now wondering as to the efficiency of heating the cylinder for HW, if that UFH circuit is open even whilst not in use.

I have no off-peak electricity tariff. And I'd been thinking about your ideal scenario explanation for when the colder days arrive, having the heating on outside of the scheduled time for the HW.

That was why I started to wonder about the ST699 being replaced, as it just doesn't allow completely separate time windows for each of the CH and the HW settings.

Whilst a better programmer with 7-day settings would be an improvement, I'm now doubting how much it's worth it for the additional cost, if the hot water flow will circulate via UFH regardless.

If your UFH zone valves are powered open then all you need to do to turn it off at times is to arrange to depower it.

I think that my logic is to what you are referring to here? Could you just clarify this for me. Does "powered open" mean they open when receiving power? To me, based on observation, it seems my actuators receive their power from the wiring box that each of the actuators and the room thermostats wire back to. So to depower, as you put it, means turning each and every thermostat off.

That's my main confusion and uncertainty at present.

Thanks.

 

[Agile]

I really meant that if they are powered open then all you need to do is to use a relay or other modification to the wiring to ensure that no power is supplied to the heating thermostats when you are heating the hot water.

To ensure you can, if you choose, have heating for longer it is essential that the water is heated at times when you would not want to use the heating such as in the middle of the night.

Have you actually checked that there is no off peak tariff available in your area from any supplier? Some might be marketed for electric car charging.

You might get what you need by a simple time clock to run the water and keeping the existing one for the CH.

 

[Jim1138]

I think I understand, so could possibly put the HW on a simple clock and leave existing programmer for CH.

Look at whether the HW schedule could be done at off peak. I'm on a fixed tariff until March. Couldn't change supplier last time, and my meter is an old analogue type. I live in an apartment, so they're all (meters) located in the undercroft garage, I guess they'd not be economy 7 etc. compatible therefore without being replaced. ?

But I could make enquiries when my fixed tariff comes to an end I suppose.

And rather than look at installing a 2-port to close off the UFH, just look at the work required to install a relay to modify the electrics to power off the heating thermostats when I'm heating the HW.

Thanks for these great pointers. Definitely food for thought.