boiler plate heat exchanger - what does it do?

latecomer

I've had a quick read up online and as it sounds like its used to exchange heat between 2 liquids I'm guessing its used to heat the hot water.

What I'm interested in is how it works - i.e. what circuit is the other liquid on? I'm presuming its not the standard central heating circuit as this is off while demand is present for the hot water.

Actually its starting to make sense as I type this - there is obviously a short internal circuit used to heat the DHW and this is what the diverter valve is used for. Is that right?

And if you want to know why I'm asking - we've got an intermittent fault with our boiler and have been given a variety of explanations (and new parts) for the issue. Basically when the there has been a prolonged demand for hot water (e.g. a long hot shower) then boiler often shuts down and needs reset.

The boiler reports a high limit protection error code (A3 on a Ferroli HE38C if you are interested - no comments on boiler please ) . One diagnosis which hasn't been explored due to the engineer being over-ruled by a manager is that the plate heat exchanger is partially blocked and this is causing the problem. Does that sound plausible?

Thanks in advance

unclebulgaria

Yep, usually a blocked plate heat exchanger may see the water temperature rise very quickly at the boiler but almost negligibly at the tap or not as much as you would think anyway.

latecomer

Thanks!

While the hot water is being used it appears to be fine, its only when switching between them, normally from DHW back to central heating that it shuts down.

And following yesterdays visit we have a new diagnosis of the ionisation switch or wiring but from the manual I reckon the guy has given the manufacturers the wrong error code...... as code A2 talks about Ionisation electrode and wiring but A3 (actual error) is High Limit Protection and talks about lack of flow.

tiggerbodhi

our Baxi exhibited the same thing, does the water get hot very quickly then cut out? the plate heat exchanger is very "fine" and blocks fairly easily, dont be conned into power flushing it wont clear a blocked HE, get it replaced, fit a magna clean and make sure the boiler is adjusted and set up correctly, mainly for the maximum flow of hot water, ours was set to only 3-4 LPM which gave nice hot water but then kept cutting out, turned up to the corect 7-8 LPM and now works fine.

If you are on a service contract the HE is not normally covered, IMHO be careful of what thye quote to replace it and fit a magna clean, will be about 20-30% more than a local chap.

latecomer

Thanks - the water doesn't usually cut out but has on occasion (usually when I'm second to the shower!). Normally it just works fine until the shower is finished and then some time later when the house starts to get cold we realise the boiler has shut down again.

We already have a magnaclean fitted but the boiler was running for some time before this was added to the system.

Apparently the flow was turned up by one of the engineers but unfortunately I wasn't there that time so have no idea what he did. I suspect he turned up the pump but could be wrong.

The work is being done under a home emergency cover of our bank account so its not costing anything yet although I suspect that its only a matter of time before they say we've reached our claim limit. I have voiced my opinion on the way the problem has been tackled so hope this will carry some weight should we hit this limit.

Holmevalleyph

Just wondering if you got the boiler fixed and what the problem was? I went to a boiler this morning with same fault

southcoastrgi

Holmevalleyph wrote: »

Just wondering if you got the boiler fixed and what the problem was? I went to a boiler this morning with same fault

maybe being a service engineer is not the right vocation for you if you have to ask a customer on the internet what is wrong with your customers boiler :eek: