Time to heat hot water cylinder

[MrTom]

Hi, me again,

So attached to my Ecotec plus 630 boiler are 11 rads and a hot water cylinder.
I was having a problem with the HW cycle taking all the heat when there was demand for CH & HW so the HW has a separate time period now.

Thing is, the HW heating period is 90 mins in the afternoon and the demand isn't satisfied in that time.
Seems too long to me, what with such a big boiler.
Flow temp from the boiler is 70c and the thermostat on the tank is 60c. Water needs to travel up 3 storeys to heat the tank. The tank has green foam insulation on it and a sticker that says 'Swift Copper Cylinders 48x18' which google leads me to believe is a 166litre tank. No idea how old it is. I'm in London so could limescale be an issue?
Might the thermostat be on the blink? If I turn the tank thermostat up and down I can hear it clicking so presume it's OK...
Or should it really take that long?

The flow and return temps from the HW tank are virtually identical, despite me turning the return valve down to practically nothing. If I trim down any more the flow stops and the boiler goes into anti-cycle mode.
Not sure if getting this sorted will help but it might explain why the HW steals all the heat when there is HW and CH demand. Think the mid position valve is doing it's job...

Anyway I'm rambling now, but any thoughts appreciated...

Cheers

 

[JohnD]

when HW is on and CH is off, are the pipes out of the 3-port valve
- hot to cylinder
- cold to rads?

Some photos would be nice

 

[D_Hailsham]

Thing is, the HW heating period is 90 mins in the afternoon and the demand isn't satisfied in that time.

Is that the only heating time during the 24 hour day?

The flow and return temps from the HW tank are virtually identical, despite me turning the return valve down to practically nothing.

How old is the cylinder?

What is the setting of parameter d.19?

If it's a old one it will only be able to absorb 2-3kW, so the boiler will be cycling a lot as 2kW is below the modulation minimum. A modern rapid recovery cylinder can handle 20kW.

Why do you need a 30kW boiler? Is the house very large and/or poorly insulated. Or is that what the installer said you needed, and you went along with him?

 

[MrTom]

JohnD: 3-port behind panels and I can't check at the mo, will check later and report back.

Is that the only heating time during the 24 hour day?

No, HW only also runs for 60 mins in the morning for showers etc

How old is the cylinder?

Don't know, we've been here 2 years and it was here when we moved in...

What is the setting of parameter d.19?

d.19 currently set to 2. Should I try something different?

If it's a old one it will only be able to absorb 2-3kW, so the boiler will be cycling a lot as 2kW is below the modulation minimum. A modern rapid recovery cylinder can handle 20kW.

Hmmm OK

Why do you need a 30kW boiler? Is the house very large and/or poorly insulated. Or is that what the installer said you needed, and you went along with him?

House is quite large, old metal farm double glazing but I've put loft insulation in. Still takes CHH 60-90mins to heat to 19c when the heating has been off all day. Probably the installer thing you said...

 

[D_Hailsham]

Hot Water
You say the boiler is set to 70C. Try 75C. The cylinder should heat up quicker and so should the house.

Central Heating
The heat loss must be very high if it's taking so long to heat the house. You really need a programmable thermostat which allows you to set a lower temperature, e.g 16C, while you are out of the house. The Honeywell CM907 would be suitable. This would replace the DT90E.

The S9400 would still be required to control the hot water times, but the heating would be set to permanently on as the CM907 would take over this function.

 

[JohnD]

If it's a old one it will only be able to absorb 2-3kW,

He says it's a Green foamed cylinder

The heat loss must be very high if it's taking so long to heat the house.

Or maybe the radiators are too small. I wonder how many cu. m of gas are used per hour while it is trying to heat the house.

Or could there be an open bypass?

 

[MrTom]

I'll try increasing the temp to 75c and see what happens

There are 3 'old rads' as I think of them (heavy, no radiating fins) which I have thought of replacing as it shouldn't cost much... Rest have fins and do get that bit hotter.

I'll think about the CM907 option. When the weather is cold I tend to leave it on all day (Eco function on the DT90E set at 18c) and the boiler doesn't seem to fire up too much so maybe that's the answer. Gas consumption isn't much higher than two separate CH programmes either which makes me think the house does retain the heat once warmed up. Should hope so as it's mid-terrace!

As far as I know there aren't any bypass valves external to the boiler...
Still need to check the mid-position valve is working properly.

Cheers all for your replies

 

[D_Hailsham]

He says it's a Green foamed cylinder

Why is the colour significant?

 

[Dan Robinson]

I think Mr D is under the impression that green foam means a certain grade of insulation

 

[ScottishGasMan]

When you say the flow and return temps to the cylinder are practically the same, are they hot? If so its not the boiler thats at fault. Possibly the cylinder is an old type as said in which case I'd personally run it at least 2 hours in the morning and 2 hours late afternoon with as much of that being outside your set radiator heating times as you can.

if its an old cylinder 90 min is nothing. Also a possibility as you first stated that the cylinder stat is not functioning properly, if you pull it off have you something to measure the temp of the cylinder at that point to tell you?

also, do you actually get plenty of hot water? as in, is it just the fact its not turning off or do you find you dont actually get enough water.

 

[Agile]

Mr D is quite right !

The green foam was used at first for the latest standard although more recently its more often been blue foam.

Regardless, its a modern cylinder which should be able to absorb about 7-8 kW depending on conditions etc.

Tony

 

[Dan Robinson]

So you've never removed a cylinder with green lagging only ½" or so thick worth a puny coil?


You should get out more

 

[JohnD]

I think Mr D is under the impression that green foam means a certain grade of insulation

wrong

however Mr D thinks that a green-foamed cylinder is not old enough to be described as "a old one it will only be able to absorb 2-3kW"

 

[MrTom]

When you say the flow and return temps to the cylinder are practically the same, are they hot? If so its not the boiler thats at fault. Possibly the cylinder is an old type as said in which case I'd personally run it at least 2 hours in the morning and 2 hours late afternoon with as much of that being outside your set radiator heating times as you can.

if its an old cylinder 90 min is nothing. Also a possibility as you first stated that the cylinder stat is not functioning properly, if you pull it off have you something to measure the temp of the cylinder at that point to tell you?

also, do you actually get plenty of hot water? as in, is it just the fact its not turning off or do you find you dont actually get enough water.

The tank flow and return pipes are hot, yes - 62 ish degrees which I figure is fine due to losses through pipework travelling up 3 storeys.
The water is hot and plentiful, I just figured that the boiler might do the job quicker. But if as you and others say it's an old coil, then perhaps it just can't absorb any more.
I will pull the thermostat off and pint the IR temp sensor at the mount point to check.

Dan_Robinson - 1/2 inch of green foam is probably about right as it goes...

Cheers all!

 

[JohnD]

Flow temp from the boiler is 70c and the thermostat on the tank is 60c.

However you say that the flow pipe by the time it reaches the cylinder is only 62C. So the heat gradient is very slight, and there will be little transfer of heat, as the cylinder nears its target temperature.

Can you insulate those long pipes better?