indirect unvented water heater Q (and wireless thermostat Q)

[nwrmartin]

Hi,

I have found these forums helpful for many years - I'm sorry I haven't registered before now!

I would be grateful for some help with some Qs about the heating system in our new house. We have an unvented indirect megaflo water heater (CL250HE) which also has two immersion heating elements, and a Worcester Bosch gas fired condensing boiler (Greenstar 30 CDi).

I understand broadly how the system works to heat our water, but I want to clarify a couple of things.

1. Our programmer has separate timers for the heating and the hot water. As far as the hot water is concerned, what will the programmer switch on and off? Is it the immersion heater which is part of the water heater (for back-up and top-up, and summer use, I guess?), or is it something else?

2. Will the boiler pump heated water through the coil in the water heater every time I switch the central heating on? In other words, do I need to switch the hot water on (using the programmer) when I have the central heating on?

3. The boiler itself has two thermostats - one for the radiators, and one for water. Does the water thermostat actually do anything? If so, how does it work, if the boiler is simply pumping water through the heater's coil in the same way (and at the same time) as it pumps water through the radiators?

4. After bleeding the radiators, I topped the boiler up so that it had 1 bar of pressure (it ended up at about 1/2 bar). Was this the right thing to do?

5. Does anyone have any tips on how long the hot water and/or the heating needs to stay on to get enough hot water for two adults and a toddler?

6. How long does water stay warm in such heaters after the heating is switched off?

Finally, I have a question about wireless thermostats. The new house has one. The previous owners kept it in their bedroom. The valves of the radiator in that room have no means of being turned by hand - only the spindles are showing. Is there any reason for this?

Related to this, this radiator seems to get much less hot. I am tempted to turn the spindles so that they are fully open. Is that wise? Is there any particular reason why this radiator would be kept cooler?

Thanks so much for your help. I am trying to get someone to come and service the boiler and heater, and I hoped hoped to pick their brains, but in London SW17 no one seems too bothered about taking on that kind of work!

 

[flameport]

1. Our programmer has separate timers for the heating and the hot water. As far as the hot water is concerned, what will the programmer switch on and off? Is it the immersion heater which is part of the water heater (for back-up and top-up, and summer use, I guess?), or is it something else?

Either setting should activate the boiler. Selecting heating will circulate heated water from the boiler through the radiators. Selecting hot water should circulate heated water from the boiler through a coil inside the hot water cylinder.

2. Will the boiler pump heated water through the coil in the water heater every time I switch the central heating on? In other words, do I need to switch the hot water on (using the programmer) when I have the central heating on?

Probably not. Some systems are set to have hot water on whenever the heating is selected, but usually they would be controlled separately.

3. The boiler itself has two thermostats - one for the radiators, and one for water. Does the water thermostat actually do anything? If so, how does it work, if the boiler is simply pumping water through the heater's coil in the same way (and at the same time) as it pumps water through the radiators?

This suggests you have a combination boiler, which heats water on demand - e.g. turn hot tap on, water flows through the boiler and is heated.
The knob controls how hot the water from the hot tap(s) is. The other one is the temperature of water in the radiators.
This is an unusual item to have in combination with a hot water cylinder. It may be that this services only one hot tap, perhaps a long way from the hot water cylinder.

Twin electric immersions is also not something you would expect to see on a cylinder heated via a gas boiler - they are normally used for electric only installations.
Hopefully they are not being used as the primary water heating, as that will cost a fortune compared with the much cheaper gas.

4. After bleeding the radiators, I topped the boiler up so that it had 1 bar of pressure (it ended up at about 1/2 bar). Was this the right thing to do?

Yes.

5. Does anyone have any tips on how long the hot water and/or the heating needs to stay on to get enough hot water for two adults and a toddler?

All depends on how large the cylinder is and how much hot water you use.

6. How long does water stay warm in such heaters after the heating is switched off?

Many hours, as they have a high level of insulation.

Room thermostats are normally placed in a room where the radiator does not have a thermostatic valve, otherwise the thermostat won't work properly. Therefore the description you have given would seem to be correct - although a bedroom is an unusual place for a room thermostat if it's the only one.

Some further investigation is required to establish exactly what type of heating system(s) you have got, as the components you have are a selection of things not normally used together.

 

[nwrmartin]

Wow, Flameport, many thanks indeed for that reply. You have really helped me out.

I have had a further look at my system on the basis of your reply, and of course everything you say is spot on. I don't need any further help, but in case anyone in future finds it helpful, here are my responses to your comments.

1. Thanks - that is indeed what happens (I'm sure you aren't surprised to hear).

2. As you say, the two systems are separate. Having the central heating on doesn't give me hot water (and, of course the opposite is true too, thankfully).

3. I def don't have a combi. Having looked closer at the manuals, the hot water thermostat and related controls only come into play if the boiler has an optional diverter valve added. Mine doesn't, so those controls don't do anything.

Nor do I have two immersion elements, only one (which I can turn on and off using a separate switch - its not hooked up to a timer).

6. I turned the water off at 7am (after being on for 1 1/2 hours). At 7pm there was no problem running a bath for my son. At 11pm plenty of hot water to wash-up for bed. At 9am the next morning, enough hot water for washing faces and hands, and at 10am enough for 1 shower. Then the water started to run less warm. So I'd say the insulation was v good - 24 hours it kept water warm, after the tank had been heated for 1 1/2 hours. V impressed!


On the thermostat, what you say makes sense. There are other rooms without thermostatic valves, but its only in the main bedroom that there is no way of opening or closing the valves by hand. I guess that was a decision made by the previous owners for whatever reason.

I think, then, that everything in the system is pretty much as it should be!

Apologies for the misinformation yesterday, and thanks again for your help.