Halstead Finest Platinum - Leak in CH Microswitch via spindl

13 Oct 2008
Reaction score
United Kingdom

My combi boiler, a Halstead Finest Platinum (LPG - 3 years old), started to leak last week and on Friday it failed to produce hot water with the indicators on 'Water pressure switch inoperative'. When I lowered the controls fascia I could see that the CH microswitch housing was full of water. I dried the microswitch and the boiler is going again, but this time I'm leaving the microswitch perspex cover open to avoid drowning the microswitch with the leak that is still present. It looks like the leak comes from the spindle of the brass component underneath, where the 2 thermistors are connected (the spindle pushes an 'arm' of the microswitch).

The only spare part available from Halstead in that area is the CH microswitch assembly, but will this part fix the leak? (I.e. does it include the component including the spindle underneath?) If it doesn't is there a way to fix the leak by flushing the boiler and unscrewing the bit underneath the microswitch and adding something like PTFE tape or boss white around the spindle? (I've got no idea of what I'm going to find the other side of the spindle) Or should the whole boiler be replaced? (I hope not!)


Sponsored Links
It's been answered on here, too, if you search...
V common problem.
Thanks Chris, I'll have a closer look - I seem to trust Google too much!

Sponsored Links

As this problem is very common and I didn't manage to get directly to the answers from Google, hopefully my own words will help a bit. The answers from the experts (with link to spare parts) were given in topic 84509.

Many thanks,

Fair try young man, but that's for the HW switch not the primary one.
I assume you're talking of part 117

The seal isn't part of the microswitch assembly spare part, OR the diverter valve repair kit...

Your spring clip is probably a rusty mess now,
The gland seal & pushrod come in the "pressure switch kit", 840501 £30 ish
Squirt WD40 into the switch . If water got in then that will too.
The switch also comes as a separate part from the £££ assembly.

Send chocolate...
You can buy the sealing gland on its own as a spare part for the Biasi M90-24 boiler.

However if you do replace it then the shaft must be completely clean as the seal has been spoilt by dirt on this.

Its all because the installer did not clean the system and add inhibitor.

Many thanks ChrisR and Agile for your help. When I've got a minute I'll drain the boiler and check the extent of the damage, then order the parts. I won't expect to have the problem fixed before a couple of weeks. When I'm done I won't forget the chocolate ;) !
Many thanks ChrisR and Agile for your help. When I've got a minute I'll drain the boiler and check the extent of the damage, then order the parts. I won't expect to have the problem fixed before a couple of weeks. When I'm done I won't forget the chocolate ;) !

What am I doing wrong then? I try to get to all broken down boilers on the same day!

Hey Tony,

I'm very grateful for your swift help, and I just mentioned the 2 weeks to give you an idea of when I would start to enquire about contact details for the chocolates!

The boiler with this leak under control is fully operational, and I haven't had a chance to drain it yet. I wasn't planning on ordering the parts (which I haven't got) with an expensive next-day delivery. I also prefer to work with a good light and plenty of time to disassemble, clean and reassemble the parts so that I don't risk breaking anything (conditions which I haven't really got in the evenings). So I thought of starting working on this the coming weekend. I understand this delay could be a bit frustrating for you, but as I said before your help won't go unnoticed.


I flushed and clean the CH circuit, then filled it up with inhibitor (Sentinel).

I also thoroughly cleaned the top of the diverting valve in the boiler. All the parts had a thin layer of sludge over them that I removed carefully, and they looked like new afterwards. Before reassembling I put silicon sealant at the bottom of the gland seal and around the pushrod and I'm glad to say that the leak is now fixed!

Thank you for your help.

If you only cleaned the deposit from the pin shaft and did not replace the gland seal then keep yoyur eye on it as it might start to leak later.

As we have to give a guarantee on our work we would always replace the gland but if you are DIYing it then you dont need to if its now stopped leaking.

Silicon sealant? :eek:
Silicone grease is the stuff, but if it's all set and working I don't suppose it'll do harm now!

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links