Downstairs rads cold when hot water on.

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Hi Guys,
Hoping someone can help.
Just recently moved in to a property so don't know a huge amount about previous works. Only been in a week.
I know the previous owners had BG home care which they used a few times to install new rads and programmer etc approx 3-4 years ago.
I will try to list the basics of the system to give an idea of layout.
It is an S plan system with expansion tank in the loft and hot water cylinder in the bathroom airing cupboard upstairs.
Magnaclean filter fitted after pump and before 2 x 2 port valves.
There is also a bypass in 15mm copper with gate valve fitted after the pump and magnaclean and bypasses the 2 x 2 port valves to the return.

Flow and return are 22mm all other pipes I can see to rads are 15mm copper coming from the floor.

I have just removed the magnaclean filter and there was quite a bit of debris on the magnet, but i'm unsure how long it has been since last cleaned. I believe this was fitted with the new rads approx 3 - 4 years ago.

The problem I have is that when heating and hot water is on the downstairs rads don't heat up or are only luke warm. With heating only on all rads heat up as normal.

Anyone know what could be causing this or any advice please?
Many thanks in advance.
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[terryplumb]

The hot water cylinder needs throttling down probably ,it's getting more than its fair share of the flow.

 

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Thanks for the reply. How open should the gate valve be? I was concerned about shutting it too much and the water not getting enough, or if i close down too much will it end up down the bypass? Thanks for the help.

 

[terryplumb]

Show pics of all Pipework around hot water cylinder / pump/ motorised valves and gate valves.

 

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Hopefully you can see the layout from these pictures. Thanks for the help.

 

[terryplumb]

Red handled gate valve ,close to the floor ,left hand side , immediately after the short pipe coming from the cylinder . Turn it clockwise ,one half turn. See if it makes a difference . Will possibly need a bit of try and see ,half turn at a time. And after making an adjustment give it 15 mins for rads to alter ,before trying again.

 

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Great thanks. I'll try it tomorrow morning, hopefully an easy fix. I'll report back with my findings. Many thanks.

 

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Thanks for the advice, that seemed to work, but now the gate valve is only open half a turn. The hot water cylinder seems to take a long time to heat up. my old house took about 40-45 minutes to heat up a 900x450 cylinder, this is taking about 2 hours to heat up a 400 x 1050 cylinder to 60 degrees C. The thermostat is set correctly and I have checked with an infrared temp gun that it does indeed turn off at 60 degrees.

I've checked the temperature at the pump is approx 80 degrees C, so the boiler is heating up, but that doesn't seem to be transferring to the hot water.
Do you have any suggestions on why it may be taking so long?
Many thanks for your help. Much appreciated.

 

[terryplumb]

How many turns have you had to do to get to where you are now ?

 

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How many turns have you had to do to get to where you are now ?

Probably about 1 full turn. Could it be that all the rads need balancing? Although when heating only on all seem to get warm at about the same rate.

 

[terryplumb]

Try opening the valve a little bit .
If all the rads heat up at same rate,when only Ch is on ,then the balancing would appear to be ok.
You could of course just have it the way it was originally ,and use the programmer to heat domestic hot water outside the central heating
" On" times.

 

[JohnD]

Your cylinder is an old Yellow Foam one. Around 30 years I think. It has a smaller heat exchange coil inside than a modern cylinder so takes longer to heat up.

What is the power of your boiler?

Long ago I had a 15kW boiler, which was only just enough, and if you had a bath on a frosty night, you could feel the house cool down.

Installing CWI reduced the heat loss and removed that problem, but the new boiler is 24kW so is ample anyway.

I calculate heat loss for whole house at 0C outside and 20C inside as 12kW now I have CWI and thicker loft insulation. It uses more at first when it is heating from cold.

The modern (blue) cylinder heats in 30minutes.

As Terry says, if you can set your timer to heat the cylinder earlier or later than the CH start, it will reduce the simultaneous load.

 

[rbranco]

I have a copper tank without foam about that size and it takes about 30-40 mins to go from 18-60.

The magnaclean seems to be installed on the wrong side of the system, it should be on the return, not the flow.

 

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Try opening the valve a little bit .
If all the rads heat up at same rate,when only Ch is on ,then the balancing would appear to be ok.
You could of course just have it the way it was originally ,and use the programmer to heat domestic hot water outside the central heating
" On" times.

Thanks, yes I will try opening a bit more and see what happens, I was thinking that if I have CH and HW on together then it may be more efficient, rather than separate, but maybe I am thinking of it wrong.

 

[terryplumb]

The difference is pretty marginal really. Do you use a lot of hot water ,baths ?? Looks like you have a shower from that cylinder ,is it pumped ?