Plate to plate HE?

[birddog]

I have a Halstead Finest Gold boiler in my house which has been finding it hard to deliver DHW. I have gradually turned down the DHW stat as when the taps are turned on fullish, the boiler cuts out and then refires 10 seconds or so later and repeats giving hot/cold alternating water.

Recently, I had noticed that an upstairs radiator was colder in the middle and decided to put some degunking jollop through the system. Unfortunately, the boiler can now be heard (I can't really describe the sound but it is just obvious it is there!) and the DHW is far worse.

CH is working fine but DHW cuts out after 10 seconds or so even when a tap is only just open. After a couple of restarts it will lockout and the overtemp button will pop out underneath. A little bit of dirty water will also momentarily dribble out from the front, left side underneath too when it does this.

From reading past posts on here, it would appear that the cause is a clogged HE. I presume it is the DHW (or plate to plate?) HE? Is there anything else that could need cleaning or replacing too at the same time?

Thank you.

 

[ChrisR]

Sounds like a serious case but I'd start with the dhwhe and see.
Not a hard job, but tape up the gubbins at the front when you undo things for access, otherwise it all just hangs on the wires .

 

[birddog]

A serious case of what? Clogging or bu##ered-ness?!

+++++++++++++++++++++++++++++++++

Where is the dribbling water likely to be coming from?

 

[ChrisR]

Just clogging, I meant.
The manual is on their website (under "discontinued") so you should be able to identify the leaky bit.

 

[birddog]

Thank you. I have telephoned Halstead tech support this morning and they have said the same thing. They suggested taking out the DHW HE and standing it for 3 hours or so in a bucket of one shot drain acid before flushing and refitting. I have found the destructions on their website so will give it a go.

Thanks again for the very speedy replies!

 

[Agile]

I think you will find that the "drain acid" is in fact an alkali and totally unsuitable for dealing with a clogged HE.

In any case standing the HE in a bucket will not give much movement of an acid through it.

Not a very good idea in my view. In fact better to just shake it under a tap to get the dirt out.

Tony

 

[oilman]

The "drain acid" I bought was sulphuric acid, and very impressive at destroying concrete. Definitely wasn't an alkali. Kettle descaler would help, but I would use citric acid, as kettle descaler is formic acid, and is toxic.

 

[Agile]

Sulphuric acid would be of some help on metal oxides but would create even more insoluble Calcium sulphate on any lime compounds.

When safe citric acid is available or rather dangerous hydrochloric acid and both will dissolve metal and calcium compounds then why use anything else? Citric acid is not very successful on lime compounds though.

If you are capable of handling warm citric acid followed by 5% cold HCl then thats about the best chemicals to use.

Tony

 

[ChrisR]

Or phosphoric acid..!
Some kettle descalers are citric acid which is OK if you pour boiling water in the other side of the hex.
Jam a funnel in to get some flow through it.
For limescale, sulphamic acid is very good. Sulphuric not.

Garden hose is worth using first...

 

[birddog]

Well, I had already dropped the HE out of the bottom of the boiler and submerged it in a bucket of the evil stuff when I read the subsequent replies! Ho hum. Anyway, after leaving it for a couple of hours, I shook the remaining loose crud out. For good measure I thought I'd soak it and rinse through once more this time with citric acid before blasting fresh water through it with a hose pipe.

It came up gleaming so I've put it back into the boiler, refilled the system and fired it up. So far (2 days) it has worked a treat - no problems maintaining hot water even with taps on full and no more dodgy noises either. Hopefully, it will last!

Thanks again for the help.

 

[ChrisR]

Well done.
Was it Sulphuric acid based stuff you used, and if so, did it cause a lot of fizzing?

 

[birddog]

yes and yes!

 

[croydoncorgi]

(various) acids, including sulphuric and hydrochloric, and (hot) citric, DO work to dissolve most blockages in secondary heat exchangers. Point to remember is that 9 times out of 10, the blockage is on the PRIMARY side of the HX and consists of iron oxides (usually magnetite) from the radiators, NOT calcium 'limescale'. Limescale will occur on the SECONDARY (output) side of the HX

IF YOU DO USE ACIDS BE EXTREMELY CAREFUL and observe sensible safety precautions. Heavy duty rubber gloves and goggles are the minimum!

 

[ollski]

or of course buy a replacement.