Upgrading System

[Sustech]

I have a Thorn M54 boiler (which looks quite old) hooked up to a primatic cylinder and 7 radiators fed off one 15mm pipe. I want to ditch the primatic cylinder for an indirect hot water cylinder, with the three way motor valve and give the radiators a chance by providing a 22mm feed for them to tee off. (bungalow with concrete floors, all radiators fed from loft).
My question revolves around the boiler heat exchanger. At one side there is a take off and return for the radiators, and on the other side a take off and return for the cylinder.
With what I have described I want to do, I will only need one feed and one return. Can I just use the one side or will this lead to localised boiling?
Can I connect both feed and returns together?

Will what I want to do make sense.
I will want to replace the boiler next year, to a different area in the house and I see the above as a way of plumbing the house with that in mind.

[Agile]

You will have to ensure the vent pipe is retained. This usually feeds via the hot water cylinder heating connection.

Otherwise no problem as long as you fit a fully pumped and controlled system.

Tony

[Sustech]

Does anyone know if this boiler can be used with a sealed pressurised system?

[Agile]

I think that you are confusing the boiler with the hot water system.

The boiler can be used to heat an unvented hot water cylinder!


But the boiler must only be used on a VENTED or open heating system.

So yuo can change the primatic for an unvented system but you will need to add a feed cistern for the heating.

Tony

[Sustech]

Looks like I am getting confused.

Can I just confirm:

Open vented: separate header tank for central heating system including indirect coil in water tank, with vent to header tank.

Sealed: no header tank, system filled from mains, no vent.

Are you saying I cannot use the second type with my Thorn boiler? (too old, or just not designed for this system?)

[Agile]

You can have an unvented hot water system.

You cannot have a sealed heating system with your boiler. It must be vented!

Tony

[Sustech]

Have done the first part of the job.
Please look at the following a tell me if the layout is correct.
www.gmsustech.co.uk/images/plumbing/hwc.gif
www.gmsustech.co.uk/images/plumbing/pump.gif
www.gmsustech.co.uk/images/plumbing/coldfeed.gif
www.gmsustech.co.uk/images/plumbing/up.gif

22mm pipes from boiler, vent straight up on the flow, inverted cold feed within 6" of the vent.
The radiators are still being fed by the one 15mm tube, as the wife wanted some heat in the house.
Is it normal for the cold feed pipe to get quite warm?
I have the pump on setting one, if I try two, I get problems, water coming out of vent pipe into tank. I tried two to see if I could get more flow to the radiators, because as before, not all radiators will work together

[Agile]

That looks generally quite good.

You could have put the cold feed closer to the tee to its right.

I am surprised you get pumping over.

I assume the pump is pumping towards the motor valve?

How high is the vent above the water line?

The water in the F&E should only be about 100 mm cold.

Tony

[Sustech]

Thanks Tony,

The pump is pumping towards the motor valve.
The vent is 2ft higher than the water line.

I suppose it is a case of balancing the rads now, as I don't think they have been done before. All the valves were open when we moved in, which is probably why a couple of rads didn't want to warm up.

[Sustech]

I have converted the vent to 22mm as per Agile's recommendation and fitted a smartfit control system. This now finishes my phase 1.

I have a lot of air in the system at the moment, which don't seem to want to go. I have read that it could be gas created within the system, as I have not put any additives in yet. This possible? (there will be some left over black stuff form the original pipework.)
What would be my course of action to get rid of the air/gas?

Also, as the wife wanted a bit more heat, I turned the boiler thermostat up a bit. B B B Bang! Major fit. Boiled over into the vent and into the F&E tank. Turned back to where it was, no probs.

I take it there is a limit to what output can be set to, as the water can only pass through the heat exchanger at a certain speed.
BTU 54000. TRV on five rads, std on two, by pass fitted and set to figure given in graphs (on an estimated flow rate) (can anyone give me a ball park figure for the flow rate for the M54?)

Many thanks.

[Agile]

You cannot measure the flow rate yourself.

It needs to be about 18 li/min but thats irrelevent.

Your problem is because you system is badly configured and you cannot increase the flow rate by setting the pump to setting two.

What you can do is to measure the flow and return temperatures.

Tony

[Sustech]

Can you give me an idea of what is badly configured, as you said that the pipework wasn't too bad.

Thanks.

[Agile]

If its pumping over on any pump setting there is a problem.

Putting the vent and feed closer would help for a start but its difficult for me to simply look at a photo and decide exactly where the fault lies.

Tony

[Sustech]

Sorry for the confusion, but it's not pumping over any more. I can run the pump on 3 if I wanted to, but it is more noisy.
The problem only occurs if I increase the boiler stat, then it boils.
I can leave the stat where it is now (around 4 out of 7) as the house seems to get to the wife's required temperature.
I was interested as to why a higher boiler temperature would cause this problem as when I had the primatic cylinder, with no pump, I could set the boiler to 7 with no problems.

[Agile]

The knob setting is arbitrary.

I cannot comment without know what flow temperature the knob positions relate to.

You would need a contact thermometer to measure the flow temperature.

Is the flow coming from the TOP of the heat exchanger and the return to the bottom?

Tony