New boiler stove on, cylinder very hot but heat sink rad is cold.. Dangerous?

[Sherlock78]

Hi,
We just lit our Snowdon 30 for the first time. Cylinder heated up well, however when I went upstairs to run the kids a bath (boiling almost) I discovered the heat sink was stone cold and water was constantly pouring out of the cylinder vent pipe (I presume?) back into the big tank.

I've been worried about this, as after looking at all the diagrams, earlier in the week I had to tell him that I thought he'd plumbed the actual stove in wrong (he'd teed the cylinder/vent pipe horizontally straight off the primary port, no rise off back of the stove), he had, and he changed it all.

I've tried bleeding the heat sink, just cold water comes out, no air.
All the pipes are the right size, however I've just seen that the flow into the rad is about 4" higher than the bottom of the water tank (on the other side of the wall), that doesn't seem right does it?
I'm going to try to get him back out tomorrow, I just want to know if you folks think it's safe to run the stove?
I've shut it down for now.
I've had old kettley rayburns before so I'm not scared of a bit of banging, but I'm just concerned that the heat sink is stone cold and I thought it was meant to be on whenever the stove is, if the hot water keeps pouring into the tank

And before you start... No, he's not hetas.
None of the 10 or so hetas guys I called (we're in rural Devon) were prepared to do the plumbing unless they fitted and/or supplied the stove too.
We've done up several houses, my husband is a very good carpenter/builder (he wont touch plumbing or electrics) and we've fitted several stoves ourselves so we weren't prepared to pay an extra 2k for them to fit the stove as well, just thought we'd get a plumber to plumb it in, the building inspector said our plan was fine, hasn't been back to inspect yet

So, 1.. should water be running constantly into the big tank?
2.. Is it safe to run (for tonight) as the cylinder is vented?
3.. Shouldn't the flow into heat sink be lower than bottom of the tank?

Many thanks

 

[tamz]

This is a big output stove (8kw room and 22kw to water). What are you heating with it?
The plumber should have fired it up to test before letting you loose on it. Keep it off until he checks it although i have doubts as to his experience of such things.
No water should be running into the big tank at any time. The expansion pipe should be into the header tank or through the roof and shouldn't be running in normal operation.
It is irrelevant where the flow to the heat sink tees off as long as it is done properly.

 

[erpkid]

Welcome to the forum.......Tamz knowledgeable and helpful as ever.

 

[Sherlock78]

I have my doubts now too.
He'd just fitted a Thermal store/solar/stove combo for someone we know so thought he would be ok, I hadn't realised what a different thing this was until I saw that stove fitters manual site.

I calculated our max requirements at 74000 btu, running dhw & 13 mostly double rads, it's 2 houses knocked into one, the room with the stove is about 9m x 10m, I did a lot of research! And we're almost entirely burning wood which brings the output down a bit.

The rad circulating pump isn't on yet as we wanted a proper sparky to wire up the stats & pumps.

Should the heat sink be hot all the time the stove is on or not?

 

[Sherlock78]

I thought the primary circuit is meant to run fine on gravity without the ch switched on.. Isn't that the point of it? so it's safe when you have a power cut?

 

[tamz]

It should be on all the time.

Don't light the stove again until it is wired as you need the pump to dissipate the extra heat into the rads.
Even a smallish wood fire in this stove will be too much for the HW cylinder as that only takes around 3kw.
Your heat leak rad should be around 2kw+ output which is a 600mmm x 1200K2.

Have a bit patience and maybe get an old head local plumber in to have a look. These are basic systems but knowing how to fit a solar panel onto a thermal store isn't much use here :wink:

 

[Sherlock78]

That's brilliant, thank you!

Our sparky is coming tomorrow, he's amazingly knowledgable about all things construction and very old school (65). Hopefully he'll see straight off what the problem is with the heat sink, I'd rather trust him than matey now I think.
I thought the whole point of having the primary gravity circuit/heat sink was that you should be able to safely run it with the pumps off (for power cuts?)
Anyhow it's off now, at least we've all had (very hot) baths for the first time in a week
Cheers

 

[Worcester]

And then people wonder we we specialise in such things, in the renewables sector multi-source set-ups are our bread and butter.

Though the OP's problem is nothing to do with a solar coil.

This should be a straighforward installtion, though it clearly hasn't been commissioned properly with all elements - stove, ch circuit, heat sink, pumps etc.

The boiler should be switched off and not used until it has been properly comissioned. You're going to need to get someone in that knows how it should all have been put together, you'll need to make sure thay have all the nescessary qualifications to do all apsects (For example we are qualified in plumbing, unvented systems, woody biomass - wood burning stoves, electrical installation, heatpumps, solar thermal, solar pv to name a few )

As Tamz says, these systems are good 'old fashioned' technology, and set up right it is unusual for them to go wrong, however set up wrong, they can be lethal bombs.

I am also worried abouth the temperature of your hot water, there should be a themostatic mixing valve on the outlet of the hot water cylinder so that no-one can get scalded.

There are other certification bodies other than HETAS for these type of boiler stoves, yes I know I'll upset a few people, there is ignorance in that you MUST be HETAS, that isn't so. HETAS do NOT have exclusivity over solid fuel, unlike GasSafe register, they are not a legal body.

 

[Sherlock78]

So.. my point that it (the primary circuit not the rads) should be able to run safely without power isn't true then??
That was the whole point of us choosing this system (as opposed to pumped thermal store) as we're up on the moors and have frequent power cuts.
Does that mean we'll need a back up generator or something.. To make it safe?
Our water is pumped from a well too, so if power fails the header tanks won't fill back up, the plumber said this shouldn't be a problem as it's such a big tank. Does that sound wrong too? Oh god.
Sorry for all the questions, you're all very helpful.

 

[tamz]

How these work when they are wired up, is you should have 2 pipe stats, 1 set high one low wired to the pump. The high limit is set from 85 - 90º and the low limit set to around 45 - 50º. You can work them quite safely with only the high limit but there is a risk of cooling the boiler too much which can cause problems with condensation.
If the heat leak rad is working and you have a big fire on you as the cylinder heats up it starts needing/taking less heat so you are depending on the heat leak rad to dissipate the heat. Eventually it will get to a stage where more heat is being generated than can be used and when the temperature of the gravity flow rises above the set point of the high limit stat, the pump will switch on pushing heat to the heating circuit cooling it down and switch back off when the temperature drops. You may not even notice the rads heating up when it does this as sometimes it is only for a few minutes at a time.
If you were to have a power cut whilst the fire was well stocked and the pump can't run, you should damp the fire down to cut back on the heat output and maybe run off some hot water from the taps.
That would normally be enough to stop it boiling over.

 

[Sherlock78]

Thanks for your replies!
I think a generator may be a good idea then or maybe a second rad.

Plumber came back today... he found a valve on the heat sink which had been closed, so that's working now!
We kept the fire going this evening, but small, the heat sink is doing it's job, nothing has vented or banged.


Which is very reassuring, because that's what I wanted to know it could do!!
just tick over SAFELY, without needing any power.

Looking forward to having all the stat controllers in, the system you describe Tamz is what we/he was planning. Hopefully the rad circuit will be working soon too!
The electrician couldn't make it. Suggested we put a plug on the ch pump so we could switch it on manually for the weekend, so stoked the fire while the plumber was here but it didn't work.. Rads F&R were both hot from stove & the pump was churning away, but no heat getting into rads at all. Very noisy boiler & lots of venting into f&e tank, so we shut it right down again..
The pump (grundfos Eco) is on the return, as per stove instructions, but the sparky said he thought they should switch it onto the flow... any advantages/disadvantages to either? It's a very long run round all the rads.
Any opinions on that if I haven't taken up too much of your time already?

 

[Worcester]

I think a generator may be a good idea then or maybe a second rad.

You shouldn't need a generator, these are supposed to be installed with a 'normally open' valve on the heat sink circuit so that gravity (thermosiphon) can do it's bit in a fail safe mode. Which is then automatically shut off when the pump is actioned (effectively a pump and zone valve by-pass) along with high and low limit pipe thermostats to kick in the pump / back-end protection as required.

This document, although originally published in 2005 by the EST / CHeSS still holds good in almost all places: http://regulations.completepicture....lers/Domestic heating- solid fuel systems.pdf the page you want is I think page 17 figure 8

(I post this here because it is freely available to anyone that looks hard enough)