New house, please help with CH and DHW system ID

[wp8800]

Hi All.

I have just moved in to a new house, and am a little confused as to how the system I have works exactly and how I can adjust it.

SYSTEM:

Boiler Potterton Suprima 50
CL145 Water tank
Room stat
Programmable potterton control model EP2002
There is a small (5 Gallonish?) tank in the loft
Electric shower

I have attached some pictures.


The 'problems' I have are:
The DHW is roasting hot
The DHW seems to 'come on' on the timer, when you select 'on' for the CH


The questions i have are:
How do I adjust the DHW temperature?
As there are only 2 adults in the house, and we are only there in the evening and weekends, whats the best thing to set the DHW to do?

We have a cold fill washing machine and dishwasher, so only use the DHW for baths really, as often the electric shower is used. And the kettle used for any hot water in kitchen.
Would it be best to just switch the DHW manually a couple of hours before we need it? (I believe the warm up time is quite short on the water tank i have)

How exactly does the boiler and water tank work together?
I had a combi in my last house. What I dont understand is if I have a water tank that heats the water, why do I need a boiler? and Vice verca.

A couple of the newer rads are fitted with TRV, but the rest are not.

The room stat is in the central hall of the bungalow (with 2 rooms in loft) so is not a bad place or general temperature guide.

Sorry for the long post, but nay help would be appreicated.

thanks

 

[gas4you]

Firstly do you mean a brand new mew build house, or new to you?

If brand new, then heating system doesn't appear to conform with Part L regs.

I will assume for now that it is new to you.

It sounds as though the 3 port zone valve is sticking open and not accepting commands from the external controls.

 

[wp8800]

Hi Dave

Yes you are right, its new to me. Not a new build.

A sticking 3 port valve will mean that the DHW and CH run together?

 

[gas4you]

Yes if its stuck in mid position.

 

[wp8800]

thanks, ill check that.

Could you explain about why i have a boiler and a heating tank?

cheers

 

[D_Hailsham]

CL145 Water tank

That's a Megaflow unvented HW cylinder. Any work involving this cylinder needs to be done by some one with G3 certification.

How do I adjust the DHW temperature?

The temperature control is hidden behind the connection panel shown in the first pic. It is just a numbered dial it should be set to 4, which is 60°C.
1 =30°C and 5=70°C

How exactly does the boiler and water tank work together?
I had a combi in my last house. What I don't understand is if I have a water tank that heats the water, why do I need a boiler? and vice versa.

How do you think the water in the tank is heated?

The hot water from the boiler comes up to the mid-position valve V4073, shown in your third pic and enters through the centre connection. This valve can direct the water to the radiators, the cylinder or both. When the hot water needs to be heated the water from the boiler is sent via the V4073 through the two port valve (lower valve in the last pic) into a coiled pipe in the HW cylinder and then back to the boiler. The heat from the boiler is then transferred, via the coil in the HW cylinder, to the rest of the water in the cylinder.

The programmer controls which port(s) of the V4073 valve is open and the HW thermostat in the CL145 controls whether the two port valve is open.

The small tank in the loft is the Feed and Expansion (F&E) tank it is used to fill the boiler, radiator and HW coil circuit and replenish if any is lost.

A couple of the newer rads are fitted with TRV, but the rest are not.

It would be a good idea to have TRVs on all rads, except where the room stat is located.

The room stat is in the central hall ... so is not a bad place or general temperature guide.

Not sure what you are saying!

 

[wp8800]

Hi, thanks for that fantastic info.

Just so im sure, and not meaning to sound thick...

I thought the water in the tank was heated by an electrically powered heating element, so therfore wondered why I would need a boiler.

But am I right in thinking that the water in the tank is heated by a coil of pipe within the tank, through which hot water runs heated by the boiler?

 

[D_Hailsham]

Just so im sure, and not meaning to sound thick...

It's called learning.

I thought the water in the tank was heated by an electrically powered heating element, so therefore wondered why I would need a boiler.

No. But an electric water heater, aka immersion heater, is sometimes fitted to the cylinder as a backup, in case the boiler etc fails.

But am I right in thinking that the water in the tank is heated by a coil of pipe within the tank, through which hot water runs heated by the boiler?

You've got it in one.

One thing, which I did not mention, is that the water being heated in the cylinder comes straight from the mains. So the water coming out of the Hot taps is at mains pressure - just like with a Combi boiler. So your system could be thought of as a combi with a very large reservoir of heated water.

 

[wp8800]

Hi Dave

Thanks for understanding my 'learning'! LOL


Just another couple of things:

If I dont ever set the DHW to come 'on' on the programmer, it should never heat the hot water right?

If right, then if i get hot water without ever setting it to come on, I have a problem? Possibly the diverter valve not closing off the connection to the hot water cylinder?


If this is the case, would it explain the roasting hot DHW? or is that simply down to changing the temp setting?


The boiler has a 'temperature' control on it as well, as I right in thinking this just controls the temperature of the water used to heat the water in the tank?


If i have a tank full of cold water, from not heating it. If i turn a hot tap on, will i never get hot water? or will the boiler be able to heat it directly?


Im really sorry to be a pain, but the couple of things im trying to sort out are:
1. the DHW temp
2. Not having 145L of hot water being kept hot and sat doing nothing for hours on end.

cheers

 

[D_Hailsham]

If I dont ever set the DHW to come 'on' on the programmer, it should never heat the hot water right?

Correct.

If right, then if i get hot water without ever setting it to come on, I have a problem? Possibly the diverter valve not closing off the connection to the hot water cylinder?

Yes. When HW is turned off at the programmer. The V4073 should close the HW (B) port, so no water circulates through the coil. For this to happen the White and Grey wires of the valve need to have 240v on them.

If this is the case, would it explain the roasting hot DHW? or is that simply down to changing the temp setting?

Even if the HW port of the V4073 is open, the other valve should still close when the hot water reaches the temperature set by the HW thermostat. If it is not closing, then either the thermostat or the valve is faulty.

The boiler has a 'temperature' control on it as well, as I right in thinking this just controls the temperature of the water used to heat the water in the tank?

Yes; and the temperature of the water circulating through the radiators. If you have a room thermostat and a working HW thermostat, the boiler stat can be set to 75-80°C and left there.

If i have a tank full of cold water, from not heating it. If i turn a hot tap on, will i never get hot water? or will the boiler be able to heat it directly?

That.s an interesting question. If the water can be heated at a fast enough rate, the water will temperature will rise until it reaches that set on the HW thermostat. It's similar to heating up a house from cold; as you heat it, the heat escapes so you have to put the heat in faster than it escapes.

1. the DHW temp
2. Not having 145L of hot water being kept hot and sat doing nothing for hours on end.

See above for item 1.

As for item 2, the rate of heat loss from your Megaflow cylinder is 1.65kWH per day, which is insignificant.

 

[wp8800]

cheers, ill see if i can check out the valve operations asap.

With ref to my no.2 problem about having hot water sat doing nothing.

Are you saying that because the tank lets the hot water cool down by such a small amount, that the boiler wont be running often to keep the water temp up?

I think ill test the theory on the cold tank and running hot water, to see what happens.

 

[D_Hailsham]

With ref to my no.2 problem about having hot water sat doing nothing.

Are you saying that because the tank lets the hot water cool down by such a small amount, that the boiler wont be running often to keep the water temp up?

Essentially, yes.

The other thing to bear in mind is the control range of the HW thermostat, which may be as much as 10°C. This means that, if you set the HW stat to 60°C, heat the water until the stat turns the boiler off, and then draw off some hot water, which gets replaced by cold, the boiler will not start up until the HW temperature has dropped to 50°C.

A difference of 10°C would not be acceptable for central heating but is quite usual for HW. Even at 50°C you would need to mix cold water with the hot for a usable bath or shower.

 

[wp8800]

brilliant, thanks for all your help Dave, really appreciated.

Ill let you know how i get on!!

 

[gas4you]

HW on all the time could simply be that you've left the immersion on without realising it.

 

[wp8800]

how can i tell if the immersion is on? Where is the switch to turn on/off?

thanks